Refactor the SrcItem object to move fields associated with subqueries out

into a separate object named Subquery. This reduces the size of the SrcItem object by about 1/3rd and provides improved performance. FossilOrigin-Name: 484bcd75bc95491d8540c791c1c4d40d996cb465839564662e14f98739699bf1
author: drh <> 2024-08-20 23:11:28 +0000
committer: drh <> 2024-08-20 23:11:28 +0000
commit: 5648d717b15c1722ff19e7af1e55d68d1d172f1d (patch)
tree: 971f2c19f00ab2073124d4ecedaa7df3f0b42509
parent: 781163aa9dce91608ba33af479564f83dda1bd40 (diff)
parent: a0651b370706e58f9014453c5f36124ca8a738c9 (diff)
download: sqlite-5648d717b15c1722ff19e7af1e55d68d1d172f1d.tar.gz
sqlite-5648d717b15c1722ff19e7af1e55d68d1d172f1d.zip
25 files changed, 667 insertions, 367 deletions
diff --git a/manifest b/manifest
index e5de88085..de163306d 100644
--- a/manifest
+++ b/manifest
@@ -1,5 +1,5 @@
-C When\sthe\sdatabase\sencoding\sis\sUTF-16LE\sand\sthe\sGLOB\soptimization\sis\sused,\nit\sis\sok\sto\suse\sthe\srange\ssearch\sover\san\sindex,\sbut\sit\sis\snot\sok\sto\ndisable\sthe\sactual\sGLOB\sfunction\scall.
-D 2024-08-20T14:12:16.713
+C Refactor\sthe\sSrcItem\sobject\sto\smove\sfields\sassociated\swith\ssubqueries\sout\ninto\sa\sseparate\sobject\snamed\sSubquery.\s\sThis\sreduces\sthe\ssize\sof\sthe\sSrcItem\nobject\sby\sabout\s1/3rd\sand\sprovides\simproved\sperformance.
+D 2024-08-20T23:11:28.443
 F .fossil-settings/empty-dirs dbb81e8fc0401ac46a1491ab34a7f2c7c0452f2f06b54ebb845d024ca8283ef1
 F .fossil-settings/ignore-glob 35175cdfcf539b2318cb04a9901442804be81cd677d8b889fcc9149c21f239ea
 F LICENSE.md df5091916dbb40e6e9686186587125e1b2ff51f022cc334e886c19a0e9982724
@@ -696,34 +696,34 @@ F sqlite.pc.in 42b7bf0d02e08b9e77734a47798d1a55a9e0716b
 F sqlite3.1 acdff36db796e2d00225b911d3047d580cd136547298435426ce9d40347973cc
 F sqlite3.pc.in 48fed132e7cb71ab676105d2a4dc77127d8c1f3a
 F sqlite_cfg.h.in baf2e409c63d4e7a765e17769b6ff17c5a82bbd9cbf1e284fd2e4cefaff3fcf2
-F src/alter.c bb663fddf1fe0e2e6d8758b2b7fb6374e7c057a6ca3955f37a48986806029765
+F src/alter.c aa93e37e4a36a0525bbb2a2aeda20d2018f0aa995542c7dc658e031375e3f532
 F src/analyze.c 30bf40ec4208ead9e977bec017bccc8a9681820936e38ca5a4a7443100a6d5c5
-F src/attach.c cc9d00d30da916ff656038211410ccf04ed784b7564639b9b61d1839ed69fd39
-F src/auth.c 19b7ccacae3dfba23fc6f1d0af68134fa216e9040e53b0681b4715445ea030b4
+F src/attach.c 08235ab62ed5ccc93c22bf36e640d19effcd632319615851bccf724ec9341333
+F src/auth.c 4c1ea890e0069ad73bead5d17a5b12c34cfa4f1a24175c8147ea439b64be271c
 F src/backup.c 5c97e8023aab1ce14a42387eb3ae00ba5a0644569e3476f38661fa6f824c3523
 F src/bitvec.c 9eac5f42c11914d5ef00a75605bb205e934f435c579687f985f1f8b0995c8645
 F src/btmutex.c 79a43670447eacc651519a429f6ece9fd638563cf95b469d6891185ddae2b522
 F src/btree.c 8b42fc7d9efdb2df05c30e8f91ff6cfbd979724ae24bf90269028468b7a13333
 F src/btree.h 55066f513eb095db935169dab1dc2f7c7a747ef223c533f5d4ad4dfed346cbd0
 F src/btreeInt.h 98aadb6dcb77b012cab2574d6a728fad56b337fc946839b9898c4b4c969e30b6
-F src/build.c 237ccc0290d131d646be722f418e92ee0a38043aee25e7dfdc75f8ce5b3abe4e
+F src/build.c c5522b5faf8128227678e194275cefaeb4d063f55dbe70bcff745f1b63a187cf
 F src/callback.c db3a45e376deff6a16c0058163fe0ae2b73a2945f3f408ca32cf74960b28d490
 F src/complete.c a3634ab1e687055cd002e11b8f43eb75c17da23e
 F src/ctime.c 64e4b1227b4ed123146f0aa2989131d1fbd9b927b11e80c9d58c6a68f9cd5ce3
 F src/date.c 89ce1ff20512a7fa5070ba6e7dd5c171148ca7d580955795bf97c79c2456144a
 F src/dbpage.c 80e46e1df623ec40486da7a5086cb723b0275a6e2a7b01d9f9b5da0f04ba2782
 F src/dbstat.c 3b677254d512fcafd4d0b341bf267b38b235ccfddbef24f9154e19360fa22e43
-F src/delete.c cb766727c78e715f9fb7ec8a7d03658ed2a3016343ca687acfcec9083cdca500
-F src/expr.c fe958028b36af640b70b2174354c044f75b8c4a4645c921592122aa2a022083a
+F src/delete.c 444c4d1eaac40103461e3b6f0881846dd3aafc1cec1dd169d3482fa331667da7
+F src/expr.c 6d5f2c38fe3ec06a7eac599dac822788b36064124e20112a844e9cd5156cb239
 F src/fault.c 460f3e55994363812d9d60844b2a6de88826e007
-F src/fkey.c 852f93c0ef995e0c2b8983059a2b97151c194cc8259e21f5bc2b7ac508348c2a
+F src/fkey.c 928ed2517e8732113d2b9821aa37af639688d752f4ea9ac6e0e393d713eeb76f
 F src/func.c 1f61e32e7a357e615b5d2e774bee563761fce4f2fd97ecb0f72c33e62a2ada5f
 F src/global.c 61a419dd9e993b9be0f91de4c4ccf322b053eb829868e089f0321dd669be3b90
 F src/hash.c 9ee4269fb1d6632a6fecfb9479c93a1f29271bddbbaf215dd60420bcb80c7220
 F src/hash.h 3340ab6e1d13e725571d7cee6d3e3135f0779a7d8e76a9ce0a85971fa3953c51
 F src/hwtime.h f9c2dfb84dce7acf95ce6d289e46f5f9d3d1afd328e53da8f8e9008e3b3caae6
 F src/in-operator.md 10cd8f4bcd225a32518407c2fb2484089112fd71
-F src/insert.c 8ff11e9e54c5fc1fe89707b3d41cf44ad2822f712bd3b5da68338ea42518847e
+F src/insert.c f8d1a0f8ee258411009c6b7f2d93170e351bd19f5ad89d57e1180644297cbe70
 F src/json.c 5b6a1d6015997b9ee848a32948720bdb26a0ef2de5a2127ebf7355ce66dbdc0d
 F src/legacy.c d7874bc885906868cd51e6c2156698f2754f02d9eee1bae2d687323c3ca8e5aa
 F src/loadext.c 7432c944ff197046d67a1207790a1b13eec4548c85a9457eb0896bb3641dfb36
@@ -753,23 +753,23 @@ F src/os_win.c 6ff43bac175bd9ed79e7c0f96840b139f2f51d01689a638fd05128becf94908a
 F src/os_win.h 7b073010f1451abe501be30d12f6bc599824944a
 F src/pager.c b08600ebf0db90b6d1e9b8b6577c6fa3877cbe1a100bd0b2899e4c6e9adad4b3
 F src/pager.h 4b1140d691860de0be1347474c51fee07d5420bd7f802d38cbab8ea4ab9f538a
-F src/parse.y 318ef86fbe358b1a93262a42e152f37b97b3fddae8d319dffbd24ce2300f6c88
+F src/parse.y 5972b7d00af4c8d96fdad781af1ea1d5d51fc3b907ad61bda60e49503274e5ed
 F src/pcache.c 588cc3c5ccaaadde689ed35ce5c5c891a1f7b1f4d1f56f6cf0143b74d8ee6484
 F src/pcache.h 1497ce1b823cf00094bb0cf3bac37b345937e6f910890c626b16512316d3abf5
 F src/pcache1.c 49516ad7718a3626f28f710fa7448ef1fce3c07fd169acbb4817341950264319
 F src/pragma.c 52bfbf6dfd668b69b5eb9bd1186e3a67367c8453807150d6e75239229924f684
 F src/pragma.h e690a356c18e98414d2e870ea791c1be1545a714ba623719deb63f7f226d8bb7
 F src/prepare.c d99931f45416652895e502328ca49fe782cfc4e1ebdcda13b3736d991ebf42ce
-F src/printf.c 8b250972305e14b365561be5117ed0fd364e4fd58968776df1ce64c6280b90f9
+F src/printf.c 6a87534ebfb9e5346011191b1f3a7ebc457f5938c7e4feeea478ecf53f6a41b2
 F src/random.c 606b00941a1d7dd09c381d3279a058d771f406c5213c9932bbd93d5587be4b9c
-F src/resolve.c 0aee8a2e5340ba95a966917305dfaff5147fcad78d0839cd364b16e4746b8bcb
+F src/resolve.c 9afed5fd7b9111633bdb74a73cdc47324e28e4dc6c27113e3e9aee38fb9422ab
 F src/rowset.c 8432130e6c344b3401a8874c3cb49fefe6873fec593294de077afea2dce5ec97
-F src/select.c 7e907830b01c7fd34968514067aed1eac13e47da4bc1a936ef2020c6b866cc08
+F src/select.c 44d135bbea93872a7318f048d9d6e566b1c3eaa92d6dabe06e4741aa78d1c1ec
 F src/shell.c.in 94571558b0fb28c37a5cf6dbd6ea27285341023a28a8cb5795cd2768fab67704
 F src/sqlite.h.in 1ad9110150773c38ebababbad11b5cb361bcd3997676dec1c91ac5e0416a7b86
 F src/sqlite3.rc 5121c9e10c3964d5755191c80dd1180c122fc3a8
 F src/sqlite3ext.h 3f046c04ea3595d6bfda99b781926b17e672fd6d27da2ba6d8d8fc39981dcb54
-F src/sqliteInt.h 128b9004698cc79993d5369d7d1763deaf8bbf26e5e8931ec540707e5a7238df
+F src/sqliteInt.h 28c878bdf528879afefe1994ac007d094f8061f2fdacdc55d6055d7e9341151e
 F src/sqliteLimit.h 6878ab64bdeb8c24a1d762d45635e34b96da21132179023338c93f820eee6728
 F src/status.c cb11f8589a6912af2da3bb1ec509a94dd8ef27df4d4c1a97e0bcf2309ece972b
 F src/table.c 0f141b58a16de7e2fbe81c308379e7279f4c6b50eb08efeec5892794a0ba30d1
@@ -828,10 +828,10 @@ F src/test_window.c 6d80e11fba89a1796525e6f0048ff0c7789aa2c6b0b11c80827dc1437bd8
 F src/test_wsd.c 41cadfd9d97fe8e3e4e44f61a4a8ccd6f7ca8fe9
 F src/threads.c 4ae07fa022a3dc7c5beb373cf744a85d3c5c6c3c
 F src/tokenize.c 3f703cacdab728d7741e5a6ac242006d74fe1c2754d4f03ed889d7253259bd68
-F src/treeview.c 774838df4e25956ca34ff79bef150266412cfc2640620d04e22d5c8a55a98992
-F src/trigger.c 0858f75818ed1580332db274f1032bcc5effe567cb132df5c5be8b1d800ca97f
-F src/update.c 732404a04d1737ef14bb6ec6b84f74edf28b3c102a92ae46b4855438a710efe7
-F src/upsert.c 2e60567a0e9e8520c18671b30712a88dc73534474304af94f32bb5f3ef65ac65
+F src/treeview.c e98dbc8068d27f3d0bd2a4cebfce6a7c21c776edc23d80e12c67a70cd2ba3fe5
+F src/trigger.c 0bb986a5b96047fd597c6aac28588853df56064e576e6b81ba777ef2ccaac461
+F src/update.c 0e01aa6a3edf9ec112b33eb714b9016a81241497b1fb7c3e74332f4f71756508
+F src/upsert.c 215328c3f91623c520ec8672c44323553f12caeb4f01b1090ebdca99fdf7b4f1
 F src/utf.c f23165685a67b4caf8ec08fb274cb3f319103decfb2a980b7cfd55d18dfa855e
 F src/util.c 5d1a0134cf4240648d1c6bb5cc8efaca0ea2b5d5c840985aec7e947271f04375
 F src/vacuum.c 604fcdaebe76f3497c855afcbf91b8fa5046b32de3045bab89cc008d68e40104
@@ -849,12 +849,12 @@ F src/vtab.c 5fb499d20494b7eecaadb7584634af9afcb374cb0524912b475fcb1712458a1b
 F src/vxworks.h d2988f4e5a61a4dfe82c6524dd3d6e4f2ce3cdb9
 F src/wal.c 887fc4ca3f020ebb2e376f222069570834ac63bf50111ef0cbf3ae417048ed89
 F src/wal.h ba252daaa94f889f4b2c17c027e823d9be47ce39da1d3799886bbd51f0490452
-F src/walker.c 7c7ea0115345851c3da4e04e2e239a29983b61fb5b038b94eede6aba462640e2
-F src/where.c f5be664f3379c9f930696e339ec4ef4c1187af860cca727411156101fae6b677
+F src/walker.c d5006d6b005e4ea7302ad390957a8d41ed83faa177e412f89bc5600a7462a014
+F src/where.c b6f79b189fcba459bb80420d3b4102f42a399be36ff29a3deff4ae4888fee46d
 F src/whereInt.h 6444b888ce395cb80511284b8a73b63472d34247fcb1b125ee06a54fa6ae878e
-F src/wherecode.c c9cac0b0b8e809c5e7e79d7796918907fb685ad99be2aaa9737f9787aa47349c
-F src/whereexpr.c 26a5a798b3f676447ae54a27584c43b32abfebb8bbcaf6faffbb7ee1da486f2d
-F src/window.c 1e40ffc509bae21e466f6106382d238e91eb73edd4ba10e66ca4fd7af2b96896
+F src/wherecode.c 137797b0de9ddf1ff43e5b0edffcc76fb05184ed651fc4f5a0a01a45c0b89d04
+F src/whereexpr.c 44f41ae554c7572e1de1485b3169b233ee04d464b2ee5881687ede3bf07cacfa
+F src/window.c 499d48f315a09242dc68f2fac635ed27dcf6bbb0d9ab9084857898c64489e975
 F test/8_3_names.test ebbb5cd36741350040fd28b432ceadf495be25b2
 F test/affinity2.test ce1aafc86e110685b324e9a763eab4f2a73f737842ec3b687bd965867de90627
 F test/affinity3.test f094773025eddf31135c7ad4cde722b7696f8eb07b97511f98585addf2a510a9
@@ -2075,7 +2075,7 @@ F test/windowerr.test a8b752402109c15aa1c5efe1b93ccb0ce1ef84fa964ae1cd6684dd0b3c
 F test/windowfault.test 15094c1529424e62f798bc679e3fe9dfab6e8ba2f7dfe8c923b6248c31660a7c
 F test/windowpushd.test c420e2265f0e09a0e798d0513a660d71b51602088d81b3dbd038918ee1339dcc
 F test/with1.test b93833890e5d2a368e78747f124503a0159aa029b98e9ed4795ebf630b2efd3d
-F test/with2.test a1df41b987198383b9b70bf5e5fda390582e46398653858dbc6ceb24253b28df
+F test/with2.test 181674a6cc86a601ca2ac052741cdfad5b529e07e870435d2f6cdb92d589ff17
 F test/with3.test e30369ea27aa27eb1bda4c5e510c8a9f782c8afd2ab99d1a02b8a7f25a5d3e65
 F test/with4.test 257be66c0c67fee1defbbac0f685c3465e2cad037f21ce65f23f86084f198205
 F test/with5.test 6248213c41fab36290b5b73aa3f937309dfba337004d9d8434c3fabc8c7d4be8
@@ -2210,8 +2210,8 @@ F vsixtest/vsixtest.tcl 6195aba1f12a5e10efc2b8c0009532167be5e301abe5b31385638080
 F vsixtest/vsixtest.vcxproj.data 2ed517e100c66dc455b492e1a33350c1b20fbcdc
 F vsixtest/vsixtest.vcxproj.filters 37e51ffedcdb064aad6ff33b6148725226cd608e
 F vsixtest/vsixtest_TemporaryKey.pfx e5b1b036facdb453873e7084e1cae9102ccc67a0
-P a5797ebdea423afc3d2d3bd8adaf1575d33a01f594c0c315afcb1499f1718e9b
-R 0a328206336eacdda27ba4526bd5a010
+P 3399698376761ab8c422f8ea02bfa2759afb606f08bedbd1cf7eee834229a9aa 4fa8235dd59cd683d6c6c97bfe181a9637be7c054d435323c903b9dbd74aff02
+R 82a6023b6446e680173d0de603e0e98e
 U drh
-Z 4c7bd06b974e78d392c3b37a21911656
+Z cc2792cc7e3d54684569210f9c97c9df
 # Remove this line to create a well-formed Fossil manifest.
diff --git a/manifest.uuid b/manifest.uuid
index 7fb9914a0..c96f75886 100644
--- a/manifest.uuid
+++ b/manifest.uuid
@@ -1 +1 @@
-3399698376761ab8c422f8ea02bfa2759afb606f08bedbd1cf7eee834229a9aa
+484bcd75bc95491d8540c791c1c4d40d996cb465839564662e14f98739699bf1
diff --git a/src/alter.c b/src/alter.c
index a8556d115..ff2075758 100644
--- a/src/alter.c
+++ b/src/alter.c
@@ -1366,8 +1366,9 @@ static int renameResolveTrigger(Parse *pParse){
           int i;
           for(i=0; i<pStep->pFrom->nSrc && rc==SQLITE_OK; i++){
             SrcItem *p = &pStep->pFrom->a[i];
-            if( p->pSelect ){
-              sqlite3SelectPrep(pParse, p->pSelect, 0);
+            if( p->fg.isSubquery ){
+              assert( p->u4.pSubq!=0 );
+              sqlite3SelectPrep(pParse, p->u4.pSubq->pSelect, 0);
             }
           }
         }
@@ -1435,8 +1436,12 @@ static void renameWalkTrigger(Walker *pWalker, Trigger *pTrigger){
     }
     if( pStep->pFrom ){
       int i;
-      for(i=0; i<pStep->pFrom->nSrc; i++){
-        sqlite3WalkSelect(pWalker, pStep->pFrom->a[i].pSelect);
+      SrcList *pFrom = pStep->pFrom;
+      for(i=0; i<pFrom->nSrc; i++){
+        if( pFrom->a[i].fg.isSubquery ){
+          assert( pFrom->a[i].u4.pSubq!=0 );
+          sqlite3WalkSelect(pWalker, pFrom->a[i].u4.pSubq->pSelect);
+        }
       }
     }
   }
@@ -1683,7 +1688,7 @@ static int renameTableSelectCb(Walker *pWalker, Select *pSelect){
   }
   for(i=0; i<pSrc->nSrc; i++){
     SrcItem *pItem = &pSrc->a[i];
-    if( pItem->pTab==p->pTab ){
+    if( pItem->pSTab==p->pTab ){
       renameTokenFind(pWalker->pParse, p, pItem->zName);
     }
   }
diff --git a/src/attach.c b/src/attach.c
index 4a6a25bf0..76476685f 100644
--- a/src/attach.c
+++ b/src/attach.c
@@ -479,20 +479,21 @@ static int fixSelectCb(Walker *p, Select *pSelect){
 
   if( NEVER(pList==0) ) return WRC_Continue;
   for(i=0, pItem=pList->a; i<pList->nSrc; i++, pItem++){
-    if( pFix->bTemp==0 ){
-      if( pItem->zDatabase ){
-        if( iDb!=sqlite3FindDbName(db, pItem->zDatabase) ){
+    if( pFix->bTemp==0 && pItem->fg.isSubquery==0 ){
+      if( pItem->fg.fixedSchema==0 && pItem->u4.zDatabase!=0 ){
+        if( iDb!=sqlite3FindDbName(db, pItem->u4.zDatabase) ){
           sqlite3ErrorMsg(pFix->pParse,
               "%s %T cannot reference objects in database %s",
-              pFix->zType, pFix->pName, pItem->zDatabase);
+              pFix->zType, pFix->pName, pItem->u4.zDatabase);
           return WRC_Abort;
         }
-        sqlite3DbFree(db, pItem->zDatabase);
-        pItem->zDatabase = 0;
+        sqlite3DbFree(db, pItem->u4.zDatabase);
         pItem->fg.notCte = 1;
+        pItem->fg.hadSchema = 1;
       }
-      pItem->pSchema = pFix->pSchema;
+      pItem->u4.pSchema = pFix->pSchema;
       pItem->fg.fromDDL = 1;
+      pItem->fg.fixedSchema = 1;
     }
 #if !defined(SQLITE_OMIT_VIEW) || !defined(SQLITE_OMIT_TRIGGER)
     if( pList->a[i].fg.isUsing==0
diff --git a/src/auth.c b/src/auth.c
index fa6c82d85..fba2c0990 100644
--- a/src/auth.c
+++ b/src/auth.c
@@ -165,7 +165,7 @@ void sqlite3AuthRead(
     assert( pTabList );
     for(iSrc=0; iSrc<pTabList->nSrc; iSrc++){
       if( pExpr->iTable==pTabList->a[iSrc].iCursor ){
-        pTab = pTabList->a[iSrc].pTab;
+        pTab = pTabList->a[iSrc].pSTab;
         break;
       }
     }
diff --git a/src/build.c b/src/build.c
index 9747810e8..74577ed0d 100644
--- a/src/build.c
+++ b/src/build.c
@@ -497,12 +497,12 @@ Table *sqlite3LocateTableItem(
   SrcItem *p
 ){
   const char *zDb;
-  assert( p->pSchema==0 || p->zDatabase==0 );
-  if( p->pSchema ){
-    int iDb = sqlite3SchemaToIndex(pParse->db, p->pSchema);
+  if( p->fg.fixedSchema ){
+    int iDb = sqlite3SchemaToIndex(pParse->db, p->u4.pSchema);
     zDb = pParse->db->aDb[iDb].zDbSName;
   }else{
-    zDb = p->zDatabase;
+    assert( !p->fg.isSubquery );
+    zDb = p->u4.zDatabase;
   }
   return sqlite3LocateTable(pParse, flags, p->zName, zDb);
 }
@@ -3487,6 +3487,8 @@ void sqlite3DropTable(Parse *pParse, SrcList *pName, int isView, int noErr){
   }
   assert( pParse->nErr==0 );
   assert( pName->nSrc==1 );
+  assert( pName->a[0].fg.fixedSchema==0 );
+  assert( pName->a[0].fg.isSubquery==0 );
   if( sqlite3ReadSchema(pParse) ) goto exit_drop_table;
   if( noErr ) db->suppressErr++;
   assert( isView==0 || isView==LOCATE_VIEW );
@@ -3495,7 +3497,7 @@ void sqlite3DropTable(Parse *pParse, SrcList *pName, int isView, int noErr){
 
   if( pTab==0 ){
     if( noErr ){
-      sqlite3CodeVerifyNamedSchema(pParse, pName->a[0].zDatabase);
+      sqlite3CodeVerifyNamedSchema(pParse, pName->a[0].u4.zDatabase);
       sqlite3ForceNotReadOnly(pParse);
     }
     goto exit_drop_table;
@@ -4586,15 +4588,17 @@ void sqlite3DropIndex(Parse *pParse, SrcList *pName, int ifExists){
   }
   assert( pParse->nErr==0 );   /* Never called with prior non-OOM errors */
   assert( pName->nSrc==1 );
+  assert( pName->a[0].fg.fixedSchema==0 );
+  assert( pName->a[0].fg.isSubquery==0 );
   if( SQLITE_OK!=sqlite3ReadSchema(pParse) ){
     goto exit_drop_index;
   }
-  pIndex = sqlite3FindIndex(db, pName->a[0].zName, pName->a[0].zDatabase);
+  pIndex = sqlite3FindIndex(db, pName->a[0].zName, pName->a[0].u4.zDatabase);
   if( pIndex==0 ){
     if( !ifExists ){
       sqlite3ErrorMsg(pParse, "no such index: %S", pName->a);
     }else{
-      sqlite3CodeVerifyNamedSchema(pParse, pName->a[0].zDatabase);
+      sqlite3CodeVerifyNamedSchema(pParse, pName->a[0].u4.zDatabase);
       sqlite3ForceNotReadOnly(pParse);
     }
     pParse->checkSchema = 1;
@@ -4891,12 +4895,14 @@ SrcList *sqlite3SrcListAppend(
   if( pDatabase && pDatabase->z==0 ){
     pDatabase = 0;
   }
+  assert( pItem->fg.fixedSchema==0 );
+  assert( pItem->fg.isSubquery==0 );
   if( pDatabase ){
     pItem->zName = sqlite3NameFromToken(db, pDatabase);
-    pItem->zDatabase = sqlite3NameFromToken(db, pTable);
+    pItem->u4.zDatabase = sqlite3NameFromToken(db, pTable);
   }else{
     pItem->zName = sqlite3NameFromToken(db, pTable);
-    pItem->zDatabase = 0;
+    pItem->u4.zDatabase = 0;
   }
   return pList;
 }
@@ -4912,14 +4918,41 @@ void sqlite3SrcListAssignCursors(Parse *pParse, SrcList *pList){
     for(i=0, pItem=pList->a; i<pList->nSrc; i++, pItem++){
       if( pItem->iCursor>=0 ) continue;
       pItem->iCursor = pParse->nTab++;
-      if( pItem->pSelect ){
-        sqlite3SrcListAssignCursors(pParse, pItem->pSelect->pSrc);
+      if( pItem->fg.isSubquery ){
+        assert( pItem->u4.pSubq!=0 );
+        assert( pItem->u4.pSubq->pSelect!=0 );
+        assert( pItem->u4.pSubq->pSelect->pSrc!=0 );
+        sqlite3SrcListAssignCursors(pParse, pItem->u4.pSubq->pSelect->pSrc);
       }
     }
   }
 }
 
 /*
+** Delete a Subquery object and its substructure.
+*/
+void sqlite3SubqueryDelete(sqlite3 *db, Subquery *pSubq){
+  assert( pSubq!=0 && pSubq->pSelect!=0 );
+  sqlite3SelectDelete(db, pSubq->pSelect);
+  sqlite3DbFree(db, pSubq);
+}
+
+/*
+** Remove a Subquery from a SrcItem.  Return the associated Select object.
+** The returned Select becomes the responsibility of the caller.
+*/
+Select *sqlite3SubqueryDetach(sqlite3 *db, SrcItem *pItem){
+  Select *pSel;
+  assert( pItem!=0 );
+  assert( pItem->fg.isSubquery );
+  pSel = pItem->u4.pSubq->pSelect;
+  sqlite3DbFree(db, pItem->u4.pSubq);
+  pItem->u4.pSubq = 0;
+  pItem->fg.isSubquery = 0;
+  return pSel;
+}
+
+/*
 ** Delete an entire SrcList including all its substructure.
 */
 void sqlite3SrcListDelete(sqlite3 *db, SrcList *pList){
@@ -4928,13 +4961,26 @@ void sqlite3SrcListDelete(sqlite3 *db, SrcList *pList){
   assert( db!=0 );
   if( pList==0 ) return;
   for(pItem=pList->a, i=0; i<pList->nSrc; i++, pItem++){
-    if( pItem->zDatabase ) sqlite3DbNNFreeNN(db, pItem->zDatabase);
+ 
+    /* Check invariants on SrcItem */
+    assert( !pItem->fg.isIndexedBy || !pItem->fg.isTabFunc );
+    assert( !pItem->fg.isCte || !pItem->fg.isIndexedBy );
+    assert( !pItem->fg.hadSchema || !pItem->fg.isSubquery );
+    assert( !pItem->fg.hadSchema || pItem->fg.fixedSchema );
+    assert( !pItem->fg.fixedSchema || !pItem->fg.isSubquery );
+    assert( !pItem->fg.isSubquery || (pItem->u4.pSubq!=0 && 
+                                      pItem->u4.pSubq->pSelect!=0) );
+
     if( pItem->zName ) sqlite3DbNNFreeNN(db, pItem->zName);
     if( pItem->zAlias ) sqlite3DbNNFreeNN(db, pItem->zAlias);
+    if( pItem->fg.isSubquery ){
+      sqlite3SubqueryDelete(db, pItem->u4.pSubq);
+    }else if( pItem->fg.fixedSchema==0 && pItem->u4.zDatabase!=0 ){
+      sqlite3DbNNFreeNN(db, pItem->u4.zDatabase);
+    }
     if( pItem->fg.isIndexedBy ) sqlite3DbFree(db, pItem->u1.zIndexedBy);
     if( pItem->fg.isTabFunc ) sqlite3ExprListDelete(db, pItem->u1.pFuncArg);
-    sqlite3DeleteTable(db, pItem->pTab);
-    if( pItem->pSelect ) sqlite3SelectDelete(db, pItem->pSelect);
+    sqlite3DeleteTable(db, pItem->pSTab);
     if( pItem->fg.isUsing ){
       sqlite3IdListDelete(db, pItem->u3.pUsing);
     }else if( pItem->u3.pOn ){
@@ -4945,6 +4991,54 @@ void sqlite3SrcListDelete(sqlite3 *db, SrcList *pList){
 }
 
 /*
+** Attach a Subquery object to pItem->uv.pSubq.  Set the
+** pSelect value but leave all the other values initialized
+** to zero.
+**
+** A copy of the Select object is made if dupSelect is true, and the
+** SrcItem takes responsibility for deleting the copy.  If dupSelect is
+** false, ownership of the Select passes to the SrcItem.  Either way,
+** the SrcItem will take responsibility for deleting the Select.
+**
+** When dupSelect is zero, that means the Select might get deleted right
+** away if there is an OOM error.  Beware.
+**
+** Return non-zero on success.  Return zero on an OOM error.
+*/
+int sqlite3SrcItemAttachSubquery(
+  Parse *pParse,     /* Parsing context */
+  SrcItem *pItem,    /* Item to which the subquery is to be attached */
+  Select *pSelect,   /* The subquery SELECT.  Must be non-NULL */
+  int dupSelect      /* If true, attach a copy of pSelect, not pSelect itself.*/
+){
+  Subquery *p;
+  assert( pSelect!=0 );
+  assert( pItem->fg.isSubquery==0 );
+  if( pItem->fg.fixedSchema ){
+    pItem->u4.pSchema = 0;
+    pItem->fg.fixedSchema = 0;
+  }else if( pItem->u4.zDatabase!=0 ){
+    sqlite3DbFree(pParse->db, pItem->u4.zDatabase);
+    pItem->u4.zDatabase = 0;
+  }
+  if( dupSelect ){
+    pSelect = sqlite3SelectDup(pParse->db, pSelect, 0);
+    if( pSelect==0 ) return 0;
+  }
+  p = pItem->u4.pSubq = sqlite3DbMallocRawNN(pParse->db, sizeof(Subquery));
+  if( p==0 ){
+    sqlite3SelectDelete(pParse->db, pSelect);
+    return 0;
+  }
+  pItem->fg.isSubquery = 1;
+  p->pSelect = pSelect;
+  assert( offsetof(Subquery, pSelect)==0 );
+  memset(((char*)p)+sizeof(p->pSelect), 0, sizeof(*p)-sizeof(p->pSelect));
+  return 1;
+}
+
+
+/*
 ** This routine is called by the parser to add a new term to the
 ** end of a growing FROM clause.  The "p" parameter is the part of
 ** the FROM clause that has already been constructed.  "p" is NULL
@@ -4993,10 +5087,12 @@ SrcList *sqlite3SrcListAppendFromTerm(
   if( pAlias->n ){
     pItem->zAlias = sqlite3NameFromToken(db, pAlias);
   }
+  assert( pSubquery==0 || pDatabase==0 );
   if( pSubquery ){
-    pItem->pSelect = pSubquery;
-    if( pSubquery->selFlags & SF_NestedFrom ){
-      pItem->fg.isNestedFrom = 1;
+    if( sqlite3SrcItemAttachSubquery(pParse, pItem, pSubquery, 0) ){
+      if( pSubquery->selFlags & SF_NestedFrom ){
+        pItem->fg.isNestedFrom = 1;
+      }
     }
   }
   assert( pOnUsing==0 || pOnUsing->pOn==0 || pOnUsing->pUsing==0 );
diff --git a/src/delete.c b/src/delete.c
index 2baff5b3d..4cdb3946e 100644
--- a/src/delete.c
+++ b/src/delete.c
@@ -24,8 +24,8 @@
 **
 ** The following fields are initialized appropriate in pSrc:
 **
-**    pSrc->a[0].pTab       Pointer to the Table object
-**    pSrc->a[0].pIndex     Pointer to the INDEXED BY index, if there is one
+**    pSrc->a[0].spTab        Pointer to the Table object
+**    pSrc->a[0].u2.pIBIndex  Pointer to the INDEXED BY index, if there is one
 **
 */
 Table *sqlite3SrcListLookup(Parse *pParse, SrcList *pSrc){
@@ -33,8 +33,8 @@ Table *sqlite3SrcListLookup(Parse *pParse, SrcList *pSrc){
   Table *pTab;
   assert( pItem && pSrc->nSrc>=1 );
   pTab = sqlite3LocateTableItem(pParse, 0, pItem);
-  if( pItem->pTab ) sqlite3DeleteTable(pParse->db, pItem->pTab);
-  pItem->pTab = pTab;
+  if( pItem->pSTab ) sqlite3DeleteTable(pParse->db, pItem->pSTab);
+  pItem->pSTab = pTab;
   pItem->fg.notCte = 1;
   if( pTab ){
     pTab->nTabRef++;
@@ -156,7 +156,8 @@ void sqlite3MaterializeView(
   if( pFrom ){
     assert( pFrom->nSrc==1 );
     pFrom->a[0].zName = sqlite3DbStrDup(db, pView->zName);
-    pFrom->a[0].zDatabase = sqlite3DbStrDup(db, db->aDb[iDb].zDbSName);
+    assert( pFrom->a[0].fg.fixedSchema==0 && pFrom->a[0].fg.isSubquery==0 );
+    pFrom->a[0].u4.zDatabase = sqlite3DbStrDup(db, db->aDb[iDb].zDbSName);
     assert( pFrom->a[0].fg.isUsing==0 );
     assert( pFrom->a[0].u3.pOn==0 );
   }
@@ -218,7 +219,7 @@ Expr *sqlite3LimitWhere(
   **   );
   */
 
-  pTab = pSrc->a[0].pTab;
+  pTab = pSrc->a[0].pSTab;
   if( HasRowid(pTab) ){
     pLhs = sqlite3PExpr(pParse, TK_ROW, 0, 0);
     pEList = sqlite3ExprListAppend(
@@ -251,9 +252,9 @@ Expr *sqlite3LimitWhere(
 
   /* duplicate the FROM clause as it is needed by both the DELETE/UPDATE tree
   ** and the SELECT subtree. */
-  pSrc->a[0].pTab = 0;
+  pSrc->a[0].pSTab = 0;
   pSelectSrc = sqlite3SrcListDup(db, pSrc, 0);
-  pSrc->a[0].pTab = pTab;
+  pSrc->a[0].pSTab = pTab;
   if( pSrc->a[0].fg.isIndexedBy ){
     assert( pSrc->a[0].fg.isCte==0 );
     pSrc->a[0].u2.pIBIndex = 0;
diff --git a/src/expr.c b/src/expr.c
index 53b0170ab..1b18828dd 100644
--- a/src/expr.c
+++ b/src/expr.c
@@ -1877,15 +1877,30 @@ SrcList *sqlite3SrcListDup(sqlite3 *db, const SrcList *p, int flags){
     SrcItem *pNewItem = &pNew->a[i];
     const SrcItem *pOldItem = &p->a[i];
     Table *pTab;
-    pNewItem->pSchema = pOldItem->pSchema;
-    pNewItem->zDatabase = sqlite3DbStrDup(db, pOldItem->zDatabase);
+    pNewItem->fg = pOldItem->fg;
+    if( pOldItem->fg.isSubquery ){
+      Subquery *pNewSubq = sqlite3DbMallocRaw(db, sizeof(Subquery));
+      if( pNewSubq==0 ){
+        assert( db->mallocFailed );
+        pNewItem->fg.isSubquery = 0;
+      }else{
+        memcpy(pNewSubq, pOldItem->u4.pSubq, sizeof(*pNewSubq));
+        pNewSubq->pSelect = sqlite3SelectDup(db, pNewSubq->pSelect, flags);
+        if( pNewSubq->pSelect==0 ){
+          sqlite3DbFree(db, pNewSubq);
+          pNewSubq = 0;
+          pNewItem->fg.isSubquery = 0;
+        }
+      }
+      pNewItem->u4.pSubq = pNewSubq;
+    }else if( pOldItem->fg.fixedSchema ){
+      pNewItem->u4.pSchema = pOldItem->u4.pSchema;
+    }else{
+      pNewItem->u4.zDatabase = sqlite3DbStrDup(db, pOldItem->u4.zDatabase);
+    }
     pNewItem->zName = sqlite3DbStrDup(db, pOldItem->zName);
     pNewItem->zAlias = sqlite3DbStrDup(db, pOldItem->zAlias);
-    pNewItem->fg = pOldItem->fg;
     pNewItem->iCursor = pOldItem->iCursor;
-    pNewItem->addrFillSub = pOldItem->addrFillSub;
-    pNewItem->regReturn = pOldItem->regReturn;
-    pNewItem->regResult = pOldItem->regResult;
     if( pNewItem->fg.isIndexedBy ){
       pNewItem->u1.zIndexedBy = sqlite3DbStrDup(db, pOldItem->u1.zIndexedBy);
     }else if( pNewItem->fg.isTabFunc ){
@@ -1898,11 +1913,10 @@ SrcList *sqlite3SrcListDup(sqlite3 *db, const SrcList *p, int flags){
     if( pNewItem->fg.isCte ){
       pNewItem->u2.pCteUse->nUse++;
     }
-    pTab = pNewItem->pTab = pOldItem->pTab;
+    pTab = pNewItem->pSTab = pOldItem->pSTab;
     if( pTab ){
       pTab->nTabRef++;
     }
-    pNewItem->pSelect = sqlite3SelectDup(db, pOldItem->pSelect, flags);
     if( pOldItem->fg.isUsing ){
       assert( pNewItem->fg.isUsing );
       pNewItem->u3.pUsing = sqlite3IdListDup(db, pOldItem->u3.pUsing);
@@ -1976,7 +1990,6 @@ Select *sqlite3SelectDup(sqlite3 *db, const Select *pDup, int flags){
     pp = &pNew->pPrior;
     pNext = pNew;
   }
-
   return pRet;
 }
 #else
@@ -2996,8 +3009,8 @@ static Select *isCandidateForInOpt(const Expr *pX){
   pSrc = p->pSrc;
   assert( pSrc!=0 );
   if( pSrc->nSrc!=1 ) return 0;          /* Single term in FROM clause */
-  if( pSrc->a[0].pSelect ) return 0;     /* FROM is not a subquery or view */
-  pTab = pSrc->a[0].pTab;
+  if( pSrc->a[0].fg.isSubquery) return 0;/* FROM is not a subquery or view */
+  pTab = pSrc->a[0].pSTab;
   assert( pTab!=0 );
   assert( !IsView(pTab)  );              /* FROM clause is not a view */
   if( IsVirtual(pTab) ) return 0;        /* FROM clause not a virtual table */
@@ -3180,7 +3193,7 @@ int sqlite3FindInIndex(
     assert( p->pEList!=0 );             /* Because of isCandidateForInOpt(p) */
     assert( p->pEList->a[0].pExpr!=0 ); /* Because of isCandidateForInOpt(p) */
     assert( p->pSrc!=0 );               /* Because of isCandidateForInOpt(p) */
-    pTab = p->pSrc->a[0].pTab;
+    pTab = p->pSrc->a[0].pSTab;
 
     /* Code an OP_Transaction and OP_TableLock for <table>. */
     iDb = sqlite3SchemaToIndex(db, pTab->pSchema);
diff --git a/src/fkey.c b/src/fkey.c
index 1efdc0bba..f1117a884 100644
--- a/src/fkey.c
+++ b/src/fkey.c
@@ -1043,9 +1043,9 @@ void sqlite3FkCheck(
     pSrc = sqlite3SrcListAppend(pParse, 0, 0, 0);
     if( pSrc ){
       SrcItem *pItem = pSrc->a;
-      pItem->pTab = pFKey->pFrom;
+      pItem->pSTab = pFKey->pFrom;
       pItem->zName = pFKey->pFrom->zName;
-      pItem->pTab->nTabRef++;
+      pItem->pSTab->nTabRef++;
       pItem->iCursor = pParse->nTab++;
   
       if( regNew!=0 ){
@@ -1337,7 +1337,8 @@ static Trigger *fkActionTrigger(
       if( pSrc ){
         assert( pSrc->nSrc==1 );
         pSrc->a[0].zName = sqlite3DbStrDup(db, zFrom);
-        pSrc->a[0].zDatabase = sqlite3DbStrDup(db, db->aDb[iDb].zDbSName);
+        assert( pSrc->a[0].fg.fixedSchema==0 && pSrc->a[0].fg.isSubquery==0 );
+        pSrc->a[0].u4.zDatabase = sqlite3DbStrDup(db, db->aDb[iDb].zDbSName);
       }
       pSelect = sqlite3SelectNew(pParse, 
           sqlite3ExprListAppend(pParse, 0, pRaise),
diff --git a/src/insert.c b/src/insert.c
index a7e94420b..d380281be 100644
--- a/src/insert.c
+++ b/src/insert.c
@@ -585,8 +585,11 @@ void sqlite3AutoincrementEnd(Parse *pParse){
 void sqlite3MultiValuesEnd(Parse *pParse, Select *pVal){
   if( ALWAYS(pVal) && pVal->pSrc->nSrc>0 ){
     SrcItem *pItem = &pVal->pSrc->a[0];
-    sqlite3VdbeEndCoroutine(pParse->pVdbe, pItem->regReturn);
-    sqlite3VdbeJumpHere(pParse->pVdbe, pItem->addrFillSub - 1);
+    assert( (pItem->fg.isSubquery && pItem->u4.pSubq!=0) || pParse->nErr );
+    if( pItem->fg.isSubquery ){
+      sqlite3VdbeEndCoroutine(pParse->pVdbe, pItem->u4.pSubq->regReturn);
+      sqlite3VdbeJumpHere(pParse->pVdbe, pItem->u4.pSubq->addrFillSub - 1);
+    }
   }
 }
 
@@ -714,6 +717,7 @@ Select *sqlite3MultiValues(Parse *pParse, Select *pLeft, ExprList *pRow){
 
       if( pRet ){
         SelectDest dest;
+        Subquery *pSubq;
         pRet->pSrc->nSrc = 1;
         pRet->pPrior = pLeft->pPrior;
         pRet->op = pLeft->op;
@@ -723,28 +727,32 @@ Select *sqlite3MultiValues(Parse *pParse, Select *pLeft, ExprList *pRow){
         assert( pLeft->pNext==0 );
         assert( pRet->pNext==0 );
         p = &pRet->pSrc->a[0];
-        p->pSelect = pLeft;
         p->fg.viaCoroutine = 1;
-        p->addrFillSub = sqlite3VdbeCurrentAddr(v) + 1;
-        p->regReturn = ++pParse->nMem;
         p->iCursor = -1;
+        assert( !p->fg.isIndexedBy && !p->fg.isTabFunc );
         p->u1.nRow = 2;
-        sqlite3VdbeAddOp3(v,OP_InitCoroutine,p->regReturn,0,p->addrFillSub);
-        sqlite3SelectDestInit(&dest, SRT_Coroutine, p->regReturn);
-
-        /* Allocate registers for the output of the co-routine. Do so so
-        ** that there are two unused registers immediately before those
-        ** used by the co-routine. This allows the code in sqlite3Insert()
-        ** to use these registers directly, instead of copying the output
-        ** of the co-routine to a separate array for processing.  */
-        dest.iSdst = pParse->nMem + 3; 
-        dest.nSdst = pLeft->pEList->nExpr;
-        pParse->nMem += 2 + dest.nSdst;
-
-        pLeft->selFlags |= SF_MultiValue;
-        sqlite3Select(pParse, pLeft, &dest);
-        p->regResult = dest.iSdst;
-        assert( pParse->nErr || dest.iSdst>0 );
+        if( sqlite3SrcItemAttachSubquery(pParse, p, pLeft, 0) ){
+          pSubq = p->u4.pSubq;
+          pSubq->addrFillSub = sqlite3VdbeCurrentAddr(v) + 1;
+          pSubq->regReturn = ++pParse->nMem;
+          sqlite3VdbeAddOp3(v, OP_InitCoroutine,
+                            pSubq->regReturn, 0, pSubq->addrFillSub);
+          sqlite3SelectDestInit(&dest, SRT_Coroutine, pSubq->regReturn);
+
+          /* Allocate registers for the output of the co-routine. Do so so
+          ** that there are two unused registers immediately before those
+          ** used by the co-routine. This allows the code in sqlite3Insert()
+          ** to use these registers directly, instead of copying the output
+          ** of the co-routine to a separate array for processing.  */
+          dest.iSdst = pParse->nMem + 3; 
+          dest.nSdst = pLeft->pEList->nExpr;
+          pParse->nMem += 2 + dest.nSdst;
+
+          pLeft->selFlags |= SF_MultiValue;
+          sqlite3Select(pParse, pLeft, &dest);
+          pSubq->regResult = dest.iSdst;
+          assert( pParse->nErr || dest.iSdst>0 );
+        }
         pLeft = pRet;
       }
     }else{
@@ -754,12 +762,18 @@ Select *sqlite3MultiValues(Parse *pParse, Select *pLeft, ExprList *pRow){
     }
   
     if( pParse->nErr==0 ){
+      Subquery *pSubq;
       assert( p!=0 );
-      if( p->pSelect->pEList->nExpr!=pRow->nExpr ){
-        sqlite3SelectWrongNumTermsError(pParse, p->pSelect);
+      assert( p->fg.isSubquery );
+      pSubq = p->u4.pSubq;
+      assert( pSubq!=0 );
+      assert( pSubq->pSelect!=0 );
+      assert( pSubq->pSelect->pEList!=0 );
+      if( pSubq->pSelect->pEList->nExpr!=pRow->nExpr ){
+        sqlite3SelectWrongNumTermsError(pParse, pSubq->pSelect);
       }else{
-        sqlite3ExprCodeExprList(pParse, pRow, p->regResult, 0, 0);
-        sqlite3VdbeAddOp1(pParse->pVdbe, OP_Yield, p->regReturn);
+        sqlite3ExprCodeExprList(pParse, pRow, pSubq->regResult, 0, 0);
+        sqlite3VdbeAddOp1(pParse->pVdbe, OP_Yield, pSubq->regReturn);
       }
     }
     sqlite3ExprListDelete(pParse->db, pRow);
@@ -1110,9 +1124,14 @@ void sqlite3Insert(
      && pSelect->pPrior==0
     ){
       SrcItem *pItem = &pSelect->pSrc->a[0];
-      dest.iSDParm = pItem->regReturn;
-      regFromSelect = pItem->regResult;
-      nColumn = pItem->pSelect->pEList->nExpr;
+      Subquery *pSubq;
+      assert( pItem->fg.isSubquery );
+      pSubq = pItem->u4.pSubq;
+      dest.iSDParm = pSubq->regReturn;
+      regFromSelect = pSubq->regResult;
+      assert( pSubq->pSelect!=0 );
+      assert( pSubq->pSelect->pEList!=0 );
+      nColumn = pSubq->pSelect->pEList->nExpr;
       ExplainQueryPlan((pParse, 0, "SCAN %S", pItem));
       if( bIdListInOrder && nColumn==pTab->nCol ){
         regData = regFromSelect;
@@ -3032,7 +3051,7 @@ static int xferOptimization(
   if( pSelect->pSrc->nSrc!=1 ){
     return 0;   /* FROM clause must have exactly one term */
   }
-  if( pSelect->pSrc->a[0].pSelect ){
+  if( pSelect->pSrc->a[0].fg.isSubquery ){
     return 0;   /* FROM clause cannot contain a subquery */
   }
   if( pSelect->pWhere ){
diff --git a/src/parse.y b/src/parse.y
index 68c00f0a7..926dd6e7d 100644
--- a/src/parse.y
+++ b/src/parse.y
@@ -740,11 +740,21 @@ seltablist(A) ::= stl_prefix(A) nm(Y) dbnm(D) LP exprlist(E) RP as(Z) on_using(N
       if( A ){
         SrcItem *pNew = &A->a[A->nSrc-1];
         SrcItem *pOld = F->a;
+        assert( pOld->fg.fixedSchema==0 );
         pNew->zName = pOld->zName;
-        pNew->zDatabase = pOld->zDatabase;
-        pNew->pSelect = pOld->pSelect;
-        if( pNew->pSelect && (pNew->pSelect->selFlags & SF_NestedFrom)!=0 ){
-          pNew->fg.isNestedFrom = 1;
+        assert( pOld->fg.fixedSchema==0 );
+        if( pOld->fg.isSubquery ){
+          pNew->fg.isSubquery = 1;
+          pNew->u4.pSubq = pOld->u4.pSubq;
+          pOld->u4.pSubq = 0;
+          pOld->fg.isSubquery = 0;
+          assert( pNew->u4.pSubq!=0 && pNew->u4.pSubq->pSelect!=0 );
+          if( (pNew->u4.pSubq->pSelect->selFlags & SF_NestedFrom)!=0 ){
+            pNew->fg.isNestedFrom = 1;
+          }
+        }else{
+          pNew->u4.zDatabase = pOld->u4.zDatabase;
+          pOld->u4.zDatabase = 0;
         }
         if( pOld->fg.isTabFunc ){
           pNew->u1.pFuncArg = pOld->u1.pFuncArg;
@@ -752,8 +762,7 @@ seltablist(A) ::= stl_prefix(A) nm(Y) dbnm(D) LP exprlist(E) RP as(Z) on_using(N
           pOld->fg.isTabFunc = 0;
           pNew->fg.isTabFunc = 1;
         }
-        pOld->zName = pOld->zDatabase = 0;
-        pOld->pSelect = 0;
+        pOld->zName = 0;
       }
       sqlite3SrcListDelete(pParse->db, F);
     }else{
diff --git a/src/printf.c b/src/printf.c
index c0dcc5d0f..a14056514 100644
--- a/src/printf.c
+++ b/src/printf.c
@@ -848,16 +848,19 @@ void sqlite3_str_vappendf(
         if( pItem->zAlias && !flag_altform2 ){
           sqlite3_str_appendall(pAccum, pItem->zAlias);
         }else if( pItem->zName ){
-          if( pItem->zDatabase ){
-            sqlite3_str_appendall(pAccum, pItem->zDatabase);
+          if( pItem->fg.fixedSchema==0
+           && pItem->fg.isSubquery==0
+           && pItem->u4.zDatabase!=0
+          ){
+            sqlite3_str_appendall(pAccum, pItem->u4.zDatabase);
             sqlite3_str_append(pAccum, ".", 1);
           }
           sqlite3_str_appendall(pAccum, pItem->zName);
         }else if( pItem->zAlias ){
           sqlite3_str_appendall(pAccum, pItem->zAlias);
-        }else{
-          Select *pSel = pItem->pSelect;
-          assert( pSel!=0 ); /* Because of tag-20240424-1 */
+        }else if( ALWAYS(pItem->fg.isSubquery) ){/* Because of tag-20240424-1 */
+          Select *pSel = pItem->u4.pSubq->pSelect;
+          assert( pSel!=0 ); 
           if( pSel->selFlags & SF_NestedFrom ){
             sqlite3_str_appendf(pAccum, "(join-%u)", pSel->selId);
           }else if( pSel->selFlags & SF_MultiValue ){
diff --git a/src/resolve.c b/src/resolve.c
index dbb54198c..6dcb4e732 100644
--- a/src/resolve.c
+++ b/src/resolve.c
@@ -215,7 +215,7 @@ static void extendFJMatch(
   if( pNew ){
     pNew->iTable = pMatch->iCursor;
     pNew->iColumn = iColumn;
-    pNew->y.pTab = pMatch->pTab;
+    pNew->y.pTab = pMatch->pSTab;
     assert( (pMatch->fg.jointype & (JT_LEFT|JT_LTORJ))!=0 );
     ExprSetProperty(pNew, EP_CanBeNull);
     *ppList = sqlite3ExprListAppend(pParse, *ppList, pNew);
@@ -346,10 +346,10 @@ static int lookupName(
     if( pSrcList ){
       for(i=0, pItem=pSrcList->a; i<pSrcList->nSrc; i++, pItem++){
         u8 hCol;
-        pTab = pItem->pTab;
+        pTab = pItem->pSTab;
         assert( pTab!=0 && pTab->zName!=0 );
         assert( pTab->nCol>0 || pParse->nErr );
-        assert( (int)pItem->fg.isNestedFrom == IsNestedFrom(pItem->pSelect) );
+        assert( (int)pItem->fg.isNestedFrom == IsNestedFrom(pItem));
         if( pItem->fg.isNestedFrom ){
           /* In this case, pItem is a subquery that has been formed from a
           ** parenthesized subset of the FROM clause terms.  Example:
@@ -358,8 +358,12 @@ static int lookupName(
           **             This pItem -------------^
           */
           int hit = 0;
-          assert( pItem->pSelect!=0 );
-          pEList = pItem->pSelect->pEList;
+          Select *pSel;
+          assert( pItem->fg.isSubquery );
+          assert( pItem->u4.pSubq!=0 );
+          pSel = pItem->u4.pSubq->pSelect;
+          assert( pSel!=0 );
+          pEList = pSel->pEList;
           assert( pEList!=0 );
           assert( pEList->nExpr==pTab->nCol );
           for(j=0; j<pEList->nExpr; j++){
@@ -483,8 +487,8 @@ static int lookupName(
           if( cntTab==0
            || (cntTab==1
                && ALWAYS(pMatch!=0)
-               && ALWAYS(pMatch->pTab!=0)
-               && (pMatch->pTab->tabFlags & TF_Ephemeral)!=0
+               && ALWAYS(pMatch->pSTab!=0)
+               && (pMatch->pSTab->tabFlags & TF_Ephemeral)!=0
                && (pTab->tabFlags & TF_Ephemeral)==0)
           ){
             cntTab = 1;
@@ -505,7 +509,7 @@ static int lookupName(
       if( pMatch ){
         pExpr->iTable = pMatch->iCursor;
         assert( ExprUseYTab(pExpr) );
-        pExpr->y.pTab = pMatch->pTab;
+        pExpr->y.pTab = pMatch->pSTab;
         if( (pMatch->fg.jointype & (JT_LEFT|JT_LTORJ))!=0 ){
           ExprSetProperty(pExpr, EP_CanBeNull);
         }
@@ -547,7 +551,7 @@ static int lookupName(
       if( (pNC->ncFlags & NC_UUpsert)!=0 && zTab!=0 ){
         Upsert *pUpsert = pNC->uNC.pUpsert;
         if( pUpsert && sqlite3StrICmp("excluded",zTab)==0 ){
-          pTab = pUpsert->pUpsertSrc->a[0].pTab;
+          pTab = pUpsert->pUpsertSrc->a[0].pSTab;
           pExpr->iTable = EXCLUDED_TABLE_NUMBER;
         }
       }
@@ -630,11 +634,11 @@ static int lookupName(
      && pMatch
      && (pNC->ncFlags & (NC_IdxExpr|NC_GenCol))==0
      && sqlite3IsRowid(zCol)
-     && ALWAYS(VisibleRowid(pMatch->pTab) || pMatch->fg.isNestedFrom)
+     && ALWAYS(VisibleRowid(pMatch->pSTab) || pMatch->fg.isNestedFrom)
     ){
       cnt = cntTab;
 #if SQLITE_ALLOW_ROWID_IN_VIEW+0==2
-      if( pMatch->pTab!=0 && IsView(pMatch->pTab) ){
+      if( pMatch->pSTab!=0 && IsView(pMatch->pSTab) ){
         eNewExprOp = TK_NULL;
       }
 #endif
@@ -871,7 +875,7 @@ Expr *sqlite3CreateColumnExpr(sqlite3 *db, SrcList *pSrc, int iSrc, int iCol){
     SrcItem *pItem = &pSrc->a[iSrc];
     Table *pTab;
     assert( ExprUseYTab(p) );
-    pTab = p->y.pTab = pItem->pTab;
+    pTab = p->y.pTab = pItem->pSTab;
     p->iTable = pItem->iCursor;
     if( p->y.pTab->iPKey==iCol ){
       p->iColumn = -1;
@@ -990,7 +994,7 @@ static int resolveExprStep(Walker *pWalker, Expr *pExpr){
       pItem = pSrcList->a;
       pExpr->op = TK_COLUMN;
       assert( ExprUseYTab(pExpr) );
-      pExpr->y.pTab = pItem->pTab;
+      pExpr->y.pTab = pItem->pSTab;
       pExpr->iTable = pItem->iCursor;
       pExpr->iColumn--;
       pExpr->affExpr = SQLITE_AFF_INTEGER;
@@ -1880,7 +1884,11 @@ static int resolveSelectStep(Walker *pWalker, Select *p){
     ** moves the pOrderBy down to the sub-query. It will be moved back
     ** after the names have been resolved.  */
     if( p->selFlags & SF_Converted ){
-      Select *pSub = p->pSrc->a[0].pSelect;
+      Select *pSub;
+      assert( p->pSrc->a[0].fg.isSubquery );
+      assert( p->pSrc->a[0].u4.pSubq!=0 );
+      pSub = p->pSrc->a[0].u4.pSubq->pSelect;
+      assert( pSub!=0 );
       assert( p->pSrc->nSrc==1 && p->pOrderBy );
       assert( pSub->pPrior && pSub->pOrderBy==0 );
       pSub->pOrderBy = p->pOrderBy;
@@ -1892,13 +1900,16 @@ static int resolveSelectStep(Walker *pWalker, Select *p){
     if( pOuterNC ) pOuterNC->nNestedSelect++;
     for(i=0; i<p->pSrc->nSrc; i++){
       SrcItem *pItem = &p->pSrc->a[i];
-      assert( pItem->zName!=0 || pItem->pSelect!=0 );/* Test of tag-20240424-1*/
-      if( pItem->pSelect && (pItem->pSelect->selFlags & SF_Resolved)==0 ){
+      assert( pItem->zName!=0
+              || pItem->fg.isSubquery );  /* Test of tag-20240424-1*/
+      if( pItem->fg.isSubquery
+       && (pItem->u4.pSubq->pSelect->selFlags & SF_Resolved)==0
+      ){
         int nRef = pOuterNC ? pOuterNC->nRef : 0;
         const char *zSavedContext = pParse->zAuthContext;
 
         if( pItem->zName ) pParse->zAuthContext = pItem->zName;
-        sqlite3ResolveSelectNames(pParse, pItem->pSelect, pOuterNC);
+        sqlite3ResolveSelectNames(pParse, pItem->u4.pSubq->pSelect, pOuterNC);
         pParse->zAuthContext = zSavedContext;
         if( pParse->nErr ) return WRC_Abort;
         assert( db->mallocFailed==0 );
@@ -2000,7 +2011,10 @@ static int resolveSelectStep(Walker *pWalker, Select *p){
     ** These integers will be replaced by copies of the corresponding result
     ** set expressions by the call to resolveOrderGroupBy() below.  */
     if( p->selFlags & SF_Converted ){
-      Select *pSub = p->pSrc->a[0].pSelect;
+      Select *pSub;
+      assert( p->pSrc->a[0].fg.isSubquery );
+      pSub = p->pSrc->a[0].u4.pSubq->pSelect;
+      assert( pSub!=0 );
       p->pOrderBy = pSub->pOrderBy;
       pSub->pOrderBy = 0;
     }
@@ -2267,7 +2281,7 @@ int sqlite3ResolveSelfReference(
   if( pTab ){
     sSrc.nSrc = 1;
     sSrc.a[0].zName = pTab->zName;
-    sSrc.a[0].pTab = pTab;
+    sSrc.a[0].pSTab = pTab;
     sSrc.a[0].iCursor = -1;
     if( pTab->pSchema!=pParse->db->aDb[1].pSchema ){
       /* Cause EP_FromDDL to be set on TK_FUNCTION nodes of non-TEMP
diff --git a/src/select.c b/src/select.c
index c1246d3c2..87bf7fac2 100644
--- a/src/select.c
+++ b/src/select.c
@@ -332,11 +332,13 @@ int sqlite3ColumnIndex(Table *pTab, const char *zCol){
 */
 void sqlite3SrcItemColumnUsed(SrcItem *pItem, int iCol){
   assert( pItem!=0 );
-  assert( (int)pItem->fg.isNestedFrom == IsNestedFrom(pItem->pSelect) );
+  assert( (int)pItem->fg.isNestedFrom == IsNestedFrom(pItem) );
   if( pItem->fg.isNestedFrom ){
     ExprList *pResults;
-    assert( pItem->pSelect!=0 );
-    pResults = pItem->pSelect->pEList;
+    assert( pItem->fg.isSubquery );
+    assert( pItem->u4.pSubq!=0 );
+    assert( pItem->u4.pSubq->pSelect!=0 );
+    pResults = pItem->u4.pSubq->pSelect->pEList;
     assert( pResults!=0 );
     assert( iCol>=0 && iCol<pResults->nExpr );
     pResults->a[iCol].fg.bUsed = 1;
@@ -370,9 +372,9 @@ static int tableAndColumnIndex(
   assert( (piTab==0)==(piCol==0) );  /* Both or neither are NULL */
 
   for(i=iStart; i<=iEnd; i++){
-    iCol = sqlite3ColumnIndex(pSrc->a[i].pTab, zCol);
+    iCol = sqlite3ColumnIndex(pSrc->a[i].pSTab, zCol);
     if( iCol>=0
-     && (bIgnoreHidden==0 || IsHiddenColumn(&pSrc->a[i].pTab->aCol[iCol])==0)
+     && (bIgnoreHidden==0 || IsHiddenColumn(&pSrc->a[i].pSTab->aCol[iCol])==0)
     ){
       if( piTab ){
         sqlite3SrcItemColumnUsed(&pSrc->a[i], iCol);
@@ -501,10 +503,10 @@ static int sqlite3ProcessJoin(Parse *pParse, Select *p){
   pLeft = &pSrc->a[0];
   pRight = &pLeft[1];
   for(i=0; i<pSrc->nSrc-1; i++, pRight++, pLeft++){
-    Table *pRightTab = pRight->pTab;
+    Table *pRightTab = pRight->pSTab;
     u32 joinType;
 
-    if( NEVER(pLeft->pTab==0 || pRightTab==0) ) continue;
+    if( NEVER(pLeft->pSTab==0 || pRightTab==0) ) continue;
     joinType = (pRight->fg.jointype & JT_OUTER)!=0 ? EP_OuterON : EP_InnerON;
 
     /* If this is a NATURAL join, synthesize an appropriate USING clause
@@ -1930,8 +1932,12 @@ static const char *columnTypeImpl(
         SrcList *pTabList = pNC->pSrcList;
         for(j=0;j<pTabList->nSrc && pTabList->a[j].iCursor!=pExpr->iTable;j++);
         if( j<pTabList->nSrc ){
-          pTab = pTabList->a[j].pTab;
-          pS = pTabList->a[j].pSelect;
+          pTab = pTabList->a[j].pSTab;
+          if( pTabList->a[j].fg.isSubquery ){
+            pS = pTabList->a[j].u4.pSubq->pSelect;
+          }else{
+            pS = 0;
+          }
         }else{
           pNC = pNC->pNext;
         }
@@ -3983,7 +3989,9 @@ static void substSelect(
     pSrc = p->pSrc;
     assert( pSrc!=0 );
     for(i=pSrc->nSrc, pItem=pSrc->a; i>0; i--, pItem++){
-      substSelect(pSubst, pItem->pSelect, 1);
+      if( pItem->fg.isSubquery ){
+        substSelect(pSubst, pItem->u4.pSubq->pSelect, 1);
+      }
       if( pItem->fg.isTabFunc ){
         substExprList(pSubst, pItem->u1.pFuncArg);
       }
@@ -4014,7 +4022,7 @@ static void recomputeColumnsUsed(
   SrcItem *pSrcItem                /* Which FROM clause item to recompute */
 ){
   Walker w;
-  if( NEVER(pSrcItem->pTab==0) ) return;
+  if( NEVER(pSrcItem->pSTab==0) ) return;
   memset(&w, 0, sizeof(w));
   w.xExprCallback = recomputeColumnsUsedExpr;
   w.xSelectCallback = sqlite3SelectWalkNoop;
@@ -4054,8 +4062,10 @@ static void srclistRenumberCursors(
         aCsrMap[pItem->iCursor+1] = pParse->nTab++;
       }
       pItem->iCursor = aCsrMap[pItem->iCursor+1];
-      for(p=pItem->pSelect; p; p=p->pPrior){
-        srclistRenumberCursors(pParse, aCsrMap, p->pSrc, -1);
+      if( pItem->fg.isSubquery ){
+        for(p=pItem->u4.pSubq->pSelect; p; p=p->pPrior){
+          srclistRenumberCursors(pParse, aCsrMap, p->pSrc, -1);
+        }
       }
     }
   }
@@ -4366,7 +4376,8 @@ static int flattenSubquery(
   assert( pSrc && iFrom>=0 && iFrom<pSrc->nSrc );
   pSubitem = &pSrc->a[iFrom];
   iParent = pSubitem->iCursor;
-  pSub = pSubitem->pSelect;
+  assert( pSubitem->fg.isSubquery );
+  pSub = pSubitem->u4.pSubq->pSelect;
   assert( pSub!=0 );
 
 #ifndef SQLITE_OMIT_WINDOWFUNC
@@ -4419,7 +4430,7 @@ static int flattenSubquery(
   */
   if( (pSubitem->fg.jointype & (JT_OUTER|JT_LTORJ))!=0 ){
     if( pSubSrc->nSrc>1                        /* (3a) */
-     || IsVirtual(pSubSrc->a[0].pTab)          /* (3b) */
+     || IsVirtual(pSubSrc->a[0].pSTab)         /* (3b) */
      || (p->selFlags & SF_Distinct)!=0         /* (3d) */
      || (pSubitem->fg.jointype & JT_RIGHT)!=0  /* (26) */
     ){
@@ -4505,14 +4516,18 @@ static int flattenSubquery(
   pParse->zAuthContext = zSavedAuthContext;
 
   /* Delete the transient structures associated with the subquery */
-  pSub1 = pSubitem->pSelect;
-  sqlite3DbFree(db, pSubitem->zDatabase);
+  
+  if( ALWAYS(pSubitem->fg.isSubquery) ){
+    pSub1 = sqlite3SubqueryDetach(db, pSubitem);
+  }else{
+    pSub1 = 0;
+  }
+  assert( pSubitem->fg.isSubquery==0 );
+  assert( pSubitem->fg.fixedSchema==0 );
   sqlite3DbFree(db, pSubitem->zName);
   sqlite3DbFree(db, pSubitem->zAlias);
-  pSubitem->zDatabase = 0;
   pSubitem->zName = 0;
   pSubitem->zAlias = 0;
-  pSubitem->pSelect = 0;
   assert( pSubitem->fg.isUsing!=0 || pSubitem->u3.pOn==0 );
 
   /* If the sub-query is a compound SELECT statement, then (by restrictions
@@ -4553,8 +4568,8 @@ static int flattenSubquery(
     ExprList *pOrderBy = p->pOrderBy;
     Expr *pLimit = p->pLimit;
     Select *pPrior = p->pPrior;
-    Table *pItemTab = pSubitem->pTab;
-    pSubitem->pTab = 0;
+    Table *pItemTab = pSubitem->pSTab;
+    pSubitem->pSTab = 0;
     p->pOrderBy = 0;
     p->pPrior = 0;
     p->pLimit = 0;
@@ -4562,7 +4577,7 @@ static int flattenSubquery(
     p->pLimit = pLimit;
     p->pOrderBy = pOrderBy;
     p->op = TK_ALL;
-    pSubitem->pTab = pItemTab;
+    pSubitem->pSTab = pItemTab;
     if( pNew==0 ){
       p->pPrior = pPrior;
     }else{
@@ -4577,11 +4592,14 @@ static int flattenSubquery(
       TREETRACE(0x4,pParse,p,("compound-subquery flattener"
                               " creates %u as peer\n",pNew->selId));
     }
-    assert( pSubitem->pSelect==0 );
+    assert( pSubitem->fg.isSubquery==0 );
   }
   sqlite3DbFree(db, aCsrMap);
   if( db->mallocFailed ){
-    pSubitem->pSelect = pSub1;
+    assert( pSubitem->fg.fixedSchema==0 );
+    assert( pSubitem->fg.isSubquery==0 );
+    assert( pSubitem->u4.zDatabase==0 );
+    sqlite3SrcItemAttachSubquery(pParse, pSubitem, pSub1, 0);
     return 1;
   }
 
@@ -4592,8 +4610,8 @@ static int flattenSubquery(
   **
   ** pSubitem->pTab is always non-NULL by test restrictions and tests above.
   */
-  if( ALWAYS(pSubitem->pTab!=0) ){
-    Table *pTabToDel = pSubitem->pTab;
+  if( ALWAYS(pSubitem->pSTab!=0) ){
+    Table *pTabToDel = pSubitem->pSTab;
     if( pTabToDel->nTabRef==1 ){
       Parse *pToplevel = sqlite3ParseToplevel(pParse);
       sqlite3ParserAddCleanup(pToplevel, sqlite3DeleteTableGeneric, pTabToDel);
@@ -4601,7 +4619,7 @@ static int flattenSubquery(
     }else{
       pTabToDel->nTabRef--;
     }
-    pSubitem->pTab = 0;
+    pSubitem->pSTab = 0;
   }
 
   /* The following loop runs once for each term in a compound-subquery
@@ -4657,8 +4675,11 @@ static int flattenSubquery(
     */
     for(i=0; i<nSubSrc; i++){
       SrcItem *pItem = &pSrc->a[i+iFrom];
-      if( pItem->fg.isUsing ) sqlite3IdListDelete(db, pItem->u3.pUsing);
       assert( pItem->fg.isTabFunc==0 );
+      assert( pItem->fg.isSubquery
+           || pItem->fg.fixedSchema
+           || pItem->u4.zDatabase==0 );
+      if( pItem->fg.isUsing ) sqlite3IdListDelete(db, pItem->u3.pUsing);
       *pItem = pSubSrc->a[i];
       pItem->fg.jointype |= ltorj;
       iNewParent = pSubSrc->a[i].iCursor;
@@ -5342,10 +5363,10 @@ static int disableUnusedSubqueryResultColumns(SrcItem *pItem){
   if( pItem->fg.isCorrelated || pItem->fg.isCte ){
     return 0;
   }
-  assert( pItem->pTab!=0 );
-  pTab = pItem->pTab;
-  assert( pItem->pSelect!=0 );
-  pSub = pItem->pSelect;
+  assert( pItem->pSTab!=0 );
+  pTab = pItem->pSTab;
+  assert( pItem->fg.isSubquery );
+  pSub = pItem->u4.pSubq->pSelect;
   assert( pSub->pEList->nExpr==pTab->nCol );
   for(pX=pSub; pX; pX=pX->pPrior){
     if( (pX->selFlags & (SF_Distinct|SF_Aggregate))!=0 ){
@@ -5474,13 +5495,13 @@ static Table *isSimpleCount(Select *p, AggInfo *pAggInfo){
   if( p->pWhere
    || p->pEList->nExpr!=1
    || p->pSrc->nSrc!=1
-   || p->pSrc->a[0].pSelect
+   || p->pSrc->a[0].fg.isSubquery
    || pAggInfo->nFunc!=1
    || p->pHaving
   ){
     return 0;
   }
-  pTab = p->pSrc->a[0].pTab;
+  pTab = p->pSrc->a[0].pSTab;
   assert( pTab!=0 );
   assert( !IsView(pTab) );
   if( !IsOrdinaryTable(pTab) ) return 0;
@@ -5505,7 +5526,7 @@ static Table *isSimpleCount(Select *p, AggInfo *pAggInfo){
 ** pFrom->pIndex and return SQLITE_OK.
 */
 int sqlite3IndexedByLookup(Parse *pParse, SrcItem *pFrom){
-  Table *pTab = pFrom->pTab;
+  Table *pTab = pFrom->pSTab;
   char *zIndexedBy = pFrom->u1.zIndexedBy;
   Index *pIdx;
   assert( pTab!=0 );
@@ -5582,7 +5603,11 @@ static int convertCompoundSelectToSubquery(Walker *pWalker, Select *p){
   if( pNew==0 ) return WRC_Abort;
   memset(&dummy, 0, sizeof(dummy));
   pNewSrc = sqlite3SrcListAppendFromTerm(pParse,0,0,0,&dummy,pNew,0);
-  if( pNewSrc==0 ) return WRC_Abort;
+  assert( pNewSrc!=0 || pParse->nErr );
+  if( pParse->nErr ){
+    sqlite3SrcListDelete(db, pNewSrc);
+    return WRC_Abort;
+  }
   *pNew = *p;
   p->pSrc = pNewSrc;
   p->pEList = sqlite3ExprListAppend(pParse, 0, sqlite3Expr(db, TK_ASTERISK, 0));
@@ -5637,7 +5662,7 @@ static struct Cte *searchWith(
 ){
   const char *zName = pItem->zName;
   With *p;
-  assert( pItem->zDatabase==0 );
+  assert( pItem->fg.fixedSchema || pItem->u4.zDatabase==0 );
   assert( zName!=0 );
   for(p=pWith; p; p=p->pOuter){
     int i;
@@ -5707,7 +5732,7 @@ static int resolveFromTermToCte(
   Cte *pCte;               /* Matched CTE (or NULL if no match) */
   With *pWith;             /* The matching WITH */
 
-  assert( pFrom->pTab==0 );
+  assert( pFrom->pSTab==0 );
   if( pParse->pWith==0 ){
     /* There are no WITH clauses in the stack.  No match is possible */
     return 0;
@@ -5717,7 +5742,8 @@ static int resolveFromTermToCte(
     ** go no further. */
     return 0;
   }
-  if( pFrom->zDatabase!=0 ){
+  assert( pFrom->fg.hadSchema==0 || pFrom->fg.notCte!=0 );
+  if( pFrom->fg.fixedSchema==0 && pFrom->u4.zDatabase!=0 ){
     /* The FROM term contains a schema qualifier (ex: main.t1) and so
     ** it cannot possibly be a CTE reference. */
     return 0;
@@ -5753,7 +5779,7 @@ static int resolveFromTermToCte(
     }
     if( cannotBeFunction(pParse, pFrom) ) return 2;
 
-    assert( pFrom->pTab==0 );
+    assert( pFrom->pSTab==0 );
     pTab = sqlite3DbMallocZero(db, sizeof(Table));
     if( pTab==0 ) return 2;
     pCteUse = pCte->pUse;
@@ -5767,26 +5793,29 @@ static int resolveFromTermToCte(
       }
       pCteUse->eM10d = pCte->eM10d;
     }
-    pFrom->pTab = pTab;
+    pFrom->pSTab = pTab;
     pTab->nTabRef = 1;
     pTab->zName = sqlite3DbStrDup(db, pCte->zName);
     pTab->iPKey = -1;
     pTab->nRowLogEst = 200; assert( 200==sqlite3LogEst(1048576) );
     pTab->tabFlags |= TF_Ephemeral | TF_NoVisibleRowid;
-    pFrom->pSelect = sqlite3SelectDup(db, pCte->pSelect, 0);
+    sqlite3SrcItemAttachSubquery(pParse, pFrom, pCte->pSelect, 1);
     if( db->mallocFailed ) return 2;
-    pFrom->pSelect->selFlags |= SF_CopyCte;
-    assert( pFrom->pSelect );
+    assert( pFrom->fg.isSubquery && pFrom->u4.pSubq );
+    pSel = pFrom->u4.pSubq->pSelect;
+    assert( pSel!=0 );
+    pSel->selFlags |= SF_CopyCte;
     if( pFrom->fg.isIndexedBy ){
       sqlite3ErrorMsg(pParse, "no such index: \"%s\"", pFrom->u1.zIndexedBy);
       return 2;
     }
+    assert( !pFrom->fg.isIndexedBy );
     pFrom->fg.isCte = 1;
     pFrom->u2.pCteUse = pCteUse;
     pCteUse->nUse++;
 
     /* Check if this is a recursive CTE. */
-    pRecTerm = pSel = pFrom->pSelect;
+    pRecTerm = pSel;
     bMayRecursive = ( pSel->op==TK_ALL || pSel->op==TK_UNION );
     while( bMayRecursive && pRecTerm->op==pSel->op ){
       int i;
@@ -5794,11 +5823,13 @@ static int resolveFromTermToCte(
       assert( pRecTerm->pPrior!=0 );
       for(i=0; i<pSrc->nSrc; i++){
         SrcItem *pItem = &pSrc->a[i];
-        if( pItem->zDatabase==0
-         && pItem->zName!=0
+        if( pItem->zName!=0
+         && !pItem->fg.hadSchema
+         && ALWAYS( !pItem->fg.isSubquery )
+         && (pItem->fg.fixedSchema || pItem->u4.zDatabase==0)
          && 0==sqlite3StrICmp(pItem->zName, pCte->zName)
         ){
-          pItem->pTab = pTab;
+          pItem->pSTab = pTab;
           pTab->nTabRef++;
           pItem->fg.isRecursive = 1;
           if( pRecTerm->selFlags & SF_Recursive ){
@@ -5900,11 +5931,14 @@ void sqlite3SelectPopWith(Walker *pWalker, Select *p){
 ** SQLITE_NOMEM.
 */
 int sqlite3ExpandSubquery(Parse *pParse, SrcItem *pFrom){
-  Select *pSel = pFrom->pSelect;
+  Select *pSel;
   Table *pTab;
 
+  assert( pFrom->fg.isSubquery );
+  assert( pFrom->u4.pSubq!=0 );
+  pSel = pFrom->u4.pSubq->pSelect;
   assert( pSel );
-  pFrom->pTab = pTab = sqlite3DbMallocZero(pParse->db, sizeof(Table));
+  pFrom->pSTab = pTab = sqlite3DbMallocZero(pParse->db, sizeof(Table));
   if( pTab==0 ) return SQLITE_NOMEM;
   pTab->nTabRef = 1;
   if( pFrom->zAlias ){
@@ -6024,33 +6058,35 @@ static int selectExpander(Walker *pWalker, Select *p){
   */
   for(i=0, pFrom=pTabList->a; i<pTabList->nSrc; i++, pFrom++){
     Table *pTab;
-    assert( pFrom->fg.isRecursive==0 || pFrom->pTab!=0 );
-    if( pFrom->pTab ) continue;
+    assert( pFrom->fg.isRecursive==0 || pFrom->pSTab!=0 );
+    if( pFrom->pSTab ) continue;
     assert( pFrom->fg.isRecursive==0 );
     if( pFrom->zName==0 ){
 #ifndef SQLITE_OMIT_SUBQUERY
-      Select *pSel = pFrom->pSelect;
+      Select *pSel;
+      assert( pFrom->fg.isSubquery && pFrom->u4.pSubq!=0 );
+      pSel = pFrom->u4.pSubq->pSelect;
       /* A sub-query in the FROM clause of a SELECT */
       assert( pSel!=0 );
-      assert( pFrom->pTab==0 );
+      assert( pFrom->pSTab==0 );
       if( sqlite3WalkSelect(pWalker, pSel) ) return WRC_Abort;
       if( sqlite3ExpandSubquery(pParse, pFrom) ) return WRC_Abort;
 #endif
 #ifndef SQLITE_OMIT_CTE
     }else if( (rc = resolveFromTermToCte(pParse, pWalker, pFrom))!=0 ){
       if( rc>1 ) return WRC_Abort;
-      pTab = pFrom->pTab;
+      pTab = pFrom->pSTab;
       assert( pTab!=0 );
 #endif
     }else{
       /* An ordinary table or view name in the FROM clause */
-      assert( pFrom->pTab==0 );
-      pFrom->pTab = pTab = sqlite3LocateTableItem(pParse, 0, pFrom);
+      assert( pFrom->pSTab==0 );
+      pFrom->pSTab = pTab = sqlite3LocateTableItem(pParse, 0, pFrom);
       if( pTab==0 ) return WRC_Abort;
       if( pTab->nTabRef>=0xffff ){
         sqlite3ErrorMsg(pParse, "too many references to \"%s\": max 65535",
            pTab->zName);
-        pFrom->pTab = 0;
+        pFrom->pSTab = 0;
         return WRC_Abort;
       }
       pTab->nTabRef++;
@@ -6062,7 +6098,7 @@ static int selectExpander(Walker *pWalker, Select *p){
         i16 nCol;
         u8 eCodeOrig = pWalker->eCode;
         if( sqlite3ViewGetColumnNames(pParse, pTab) ) return WRC_Abort;
-        assert( pFrom->pSelect==0 );
+        assert( pFrom->fg.isSubquery==0 );
         if( IsView(pTab) ){
           if( (db->flags & SQLITE_EnableView)==0
            && pTab->pSchema!=db->aDb[1].pSchema
@@ -6070,7 +6106,7 @@ static int selectExpander(Walker *pWalker, Select *p){
             sqlite3ErrorMsg(pParse, "access to view \"%s\" prohibited",
               pTab->zName);
           }
-          pFrom->pSelect = sqlite3SelectDup(db, pTab->u.view.pSelect, 0);
+          sqlite3SrcItemAttachSubquery(pParse, pFrom, pTab->u.view.pSelect, 1);
         }
 #ifndef SQLITE_OMIT_VIRTUALTABLE
         else if( ALWAYS(IsVirtual(pTab))
@@ -6086,7 +6122,9 @@ static int selectExpander(Walker *pWalker, Select *p){
         nCol = pTab->nCol;
         pTab->nCol = -1;
         pWalker->eCode = 1;  /* Turn on Select.selId renumbering */
-        sqlite3WalkSelect(pWalker, pFrom->pSelect);
+        if( pFrom->fg.isSubquery ){
+          sqlite3WalkSelect(pWalker, pFrom->u4.pSubq->pSelect);
+        }
         pWalker->eCode = eCodeOrig;
         pTab->nCol = nCol;
       }
@@ -6173,7 +6211,7 @@ static int selectExpander(Walker *pWalker, Select *p){
         }
         for(i=0, pFrom=pTabList->a; i<pTabList->nSrc; i++, pFrom++){
           int nAdd;                    /* Number of cols including rowid */
-          Table *pTab = pFrom->pTab;   /* Table for this data source */
+          Table *pTab = pFrom->pSTab;  /* Table for this data source */
           ExprList *pNestedFrom;       /* Result-set of a nested FROM clause */
           char *zTabName;              /* AS name for this data source */
           const char *zSchemaName = 0; /* Schema name for this data source */
@@ -6184,10 +6222,11 @@ static int selectExpander(Walker *pWalker, Select *p){
             zTabName = pTab->zName;
           }
           if( db->mallocFailed ) break;
-          assert( (int)pFrom->fg.isNestedFrom == IsNestedFrom(pFrom->pSelect) );
+          assert( (int)pFrom->fg.isNestedFrom == IsNestedFrom(pFrom) );
           if( pFrom->fg.isNestedFrom ){
-            assert( pFrom->pSelect!=0 );
-            pNestedFrom = pFrom->pSelect->pEList;
+            assert( pFrom->fg.isSubquery && pFrom->u4.pSubq );
+            assert( pFrom->u4.pSubq->pSelect!=0 );
+            pNestedFrom = pFrom->u4.pSubq->pSelect->pEList;
             assert( pNestedFrom!=0 );
             assert( pNestedFrom->nExpr==pTab->nCol );
             assert( VisibleRowid(pTab)==0 || ViewCanHaveRowid );
@@ -6426,14 +6465,12 @@ static void selectAddSubqueryTypeInfo(Walker *pWalker, Select *p){
   assert( (p->selFlags & SF_Resolved) );
   pTabList = p->pSrc;
   for(i=0, pFrom=pTabList->a; i<pTabList->nSrc; i++, pFrom++){
-    Table *pTab = pFrom->pTab;
+    Table *pTab = pFrom->pSTab;
     assert( pTab!=0 );
-    if( (pTab->tabFlags & TF_Ephemeral)!=0 ){
+    if( (pTab->tabFlags & TF_Ephemeral)!=0 && pFrom->fg.isSubquery ){
       /* A sub-query in the FROM clause of a SELECT */
-      Select *pSel = pFrom->pSelect;
-      if( pSel ){
-        sqlite3SubqueryColumnTypes(pParse, pTab, pSel, SQLITE_AFF_NONE);
-      }
+      Select *pSel = pFrom->u4.pSubq->pSelect;
+      sqlite3SubqueryColumnTypes(pParse, pTab, pSel, SQLITE_AFF_NONE);
     }
   }
 }
@@ -7083,25 +7120,28 @@ static SrcItem *isSelfJoinView(
   int iFirst, int iEnd        /* Range of FROM-clause entries to search. */
 ){
   SrcItem *pItem;
-  assert( pThis->pSelect!=0 );
-  if( pThis->pSelect->selFlags & SF_PushDown ) return 0;
+  Select *pSel;
+  assert( pThis->fg.isSubquery );
+  pSel = pThis->u4.pSubq->pSelect;
+  assert( pSel!=0 );
+  if( pSel->selFlags & SF_PushDown ) return 0;
   while( iFirst<iEnd ){
     Select *pS1;
     pItem = &pTabList->a[iFirst++];
-    if( pItem->pSelect==0 ) continue;
+    if( !pItem->fg.isSubquery ) continue;
     if( pItem->fg.viaCoroutine ) continue;
     if( pItem->zName==0 ) continue;
-    assert( pItem->pTab!=0 );
-    assert( pThis->pTab!=0 );
-    if( pItem->pTab->pSchema!=pThis->pTab->pSchema ) continue;
+    assert( pItem->pSTab!=0 );
+    assert( pThis->pSTab!=0 );
+    if( pItem->pSTab->pSchema!=pThis->pSTab->pSchema ) continue;
     if( sqlite3_stricmp(pItem->zName, pThis->zName)!=0 ) continue;
-    pS1 = pItem->pSelect;
-    if( pItem->pTab->pSchema==0 && pThis->pSelect->selId!=pS1->selId ){
+    pS1 = pItem->u4.pSubq->pSelect;
+    if( pItem->pSTab->pSchema==0 && pSel->selId!=pS1->selId ){
       /* The query flattener left two different CTE tables with identical
       ** names in the same FROM clause. */
       continue;
     }
-    if( pItem->pSelect->selFlags & SF_PushDown ){
+    if( pS1->selFlags & SF_PushDown ){
       /* The view was modified by some other optimization such as
       ** pushDownWhereTerms() */
       continue;
@@ -7145,6 +7185,7 @@ static int countOfViewOptimization(Parse *pParse, Select *p){
   Expr *pExpr;
   Expr *pCount;
   sqlite3 *db;
+  SrcItem *pFrom;
   if( (p->selFlags & SF_Aggregate)==0 ) return 0;   /* This is an aggregate */
   if( p->pEList->nExpr!=1 ) return 0;               /* Single result column */
   if( p->pWhere ) return 0;
@@ -7159,8 +7200,9 @@ static int countOfViewOptimization(Parse *pParse, Select *p){
   if( pExpr->x.pList!=0 ) return 0;                 /* Must be count(*) */
   if( p->pSrc->nSrc!=1 ) return 0;                  /* One table in FROM  */
   if( ExprHasProperty(pExpr, EP_WinFunc) ) return 0;/* Not a window function */
-  pSub = p->pSrc->a[0].pSelect;
-  if( pSub==0 ) return 0;                           /* The FROM is a subquery */
+  pFrom = p->pSrc->a;
+  if( pFrom->fg.isSubquery==0 ) return 0;    /* FROM is a subquery */
+  pSub = pFrom->u4.pSubq->pSelect;
   if( pSub->pPrior==0 ) return 0;                   /* Must be a compound */
   if( pSub->selFlags & SF_CopyCte ) return 0;       /* Not a CTE */
   do{
@@ -7169,7 +7211,7 @@ static int countOfViewOptimization(Parse *pParse, Select *p){
     if( pSub->pLimit ) return 0;                      /* No LIMIT clause */
     if( pSub->selFlags & SF_Aggregate ) return 0;     /* Not an aggregate */
     assert( pSub->pHaving==0 );  /* Due to the previous */
-   pSub = pSub->pPrior;                              /* Repeat over compound */
+    pSub = pSub->pPrior;                              /* Repeat over compound */
   }while( pSub );
 
   /* If we reach this point then it is OK to perform the transformation */
@@ -7177,8 +7219,7 @@ static int countOfViewOptimization(Parse *pParse, Select *p){
   db = pParse->db;
   pCount = pExpr;
   pExpr = 0;
-  pSub = p->pSrc->a[0].pSelect;
-  p->pSrc->a[0].pSelect = 0;
+  pSub = sqlite3SubqueryDetach(db, pFrom);
   sqlite3SrcListDelete(db, p->pSrc);
   p->pSrc = sqlite3DbMallocZero(pParse->db, sizeof(*p->pSrc));
   while( pSub ){
@@ -7223,12 +7264,12 @@ static int sameSrcAlias(SrcItem *p0, SrcList *pSrc){
   for(i=0; i<pSrc->nSrc; i++){
     SrcItem *p1 = &pSrc->a[i];
     if( p1==p0 ) continue;
-    if( p0->pTab==p1->pTab && 0==sqlite3_stricmp(p0->zAlias, p1->zAlias) ){
+    if( p0->pSTab==p1->pSTab && 0==sqlite3_stricmp(p0->zAlias, p1->zAlias) ){
       return 1;
     }
-    if( p1->pSelect
-     && (p1->pSelect->selFlags & SF_NestedFrom)!=0
-     && sameSrcAlias(p0, p1->pSelect->pSrc)
+    if( p1->fg.isSubquery
+     && (p1->u4.pSubq->pSelect->selFlags & SF_NestedFrom)!=0
+     && sameSrcAlias(p0, p1->u4.pSubq->pSelect->pSrc)
     ){
       return 1;
     }
@@ -7293,7 +7334,7 @@ static int fromClauseTermCanBeCoroutine(
     if( i==0 ) break;
     i--;
     pItem--;
-    if( pItem->pSelect!=0 ) return 0;                             /* (1c-i) */
+    if( pItem->fg.isSubquery ) return 0;                          /* (1c-i) */
   }
   return 1;
 }
@@ -7404,7 +7445,7 @@ int sqlite3Select(
     if( sameSrcAlias(p0, p->pSrc) ){
       sqlite3ErrorMsg(pParse,
           "target object/alias may not appear in FROM clause: %s",
-          p0->zAlias ? p0->zAlias : p0->pTab->zName
+          p0->zAlias ? p0->zAlias : p0->pSTab->zName
       );
       goto select_end;
     }
@@ -7443,8 +7484,8 @@ int sqlite3Select(
 #if !defined(SQLITE_OMIT_SUBQUERY) || !defined(SQLITE_OMIT_VIEW)
   for(i=0; !p->pPrior && i<pTabList->nSrc; i++){
     SrcItem *pItem = &pTabList->a[i];
-    Select *pSub = pItem->pSelect;
-    Table *pTab = pItem->pTab;
+    Select *pSub = pItem->fg.isSubquery ? pItem->u4.pSubq->pSelect : 0;
+    Table *pTab = pItem->pSTab;
 
     /* The expander should have already created transient Table objects
     ** even for FROM clause elements such as subqueries that do not correspond
@@ -7662,6 +7703,7 @@ int sqlite3Select(
     SrcItem *pItem = &pTabList->a[i];
     SrcItem *pPrior;
     SelectDest dest;
+    Subquery *pSubq;
     Select *pSub;
 #if !defined(SQLITE_OMIT_SUBQUERY) || !defined(SQLITE_OMIT_VIEW)
     const char *zSavedAuthContext;
@@ -7684,17 +7726,29 @@ int sqlite3Select(
     ** string for the fake column name seems safer.
     */
     if( pItem->colUsed==0 && pItem->zName!=0 ){
-      sqlite3AuthCheck(pParse, SQLITE_READ, pItem->zName, "", pItem->zDatabase);
+      const char *zDb;
+      if( pItem->fg.fixedSchema ){
+        int iDb = sqlite3SchemaToIndex(pParse->db, pItem->u4.pSchema);
+        zDb = db->aDb[iDb].zDbSName;
+      }else if( pItem->fg.isSubquery ){
+        zDb = 0;
+      }else{
+        zDb = pItem->u4.zDatabase;
+      }
+      sqlite3AuthCheck(pParse, SQLITE_READ, pItem->zName, "", zDb);
     }
 
 #if !defined(SQLITE_OMIT_SUBQUERY) || !defined(SQLITE_OMIT_VIEW)
     /* Generate code for all sub-queries in the FROM clause
     */
-    pSub = pItem->pSelect;
-    if( pSub==0 || pItem->addrFillSub!=0 ) continue;
+    if( pItem->fg.isSubquery==0 ) continue;
+    pSubq = pItem->u4.pSubq;
+    assert( pSubq!=0 );
+    pSub = pSubq->pSelect;
+    if( pSubq->addrFillSub!=0 ) continue;
 
     /* The code for a subquery should only be generated once. */
-    assert( pItem->addrFillSub==0 );
+    assert( pSubq->addrFillSub==0 );
 
     /* Increment Parse.nHeight by the height of the largest expression
     ** tree referred to by this, the parent select. The child select
@@ -7720,7 +7774,7 @@ int sqlite3Select(
         sqlite3TreeViewSelect(0, p, 0);
       }
 #endif
-      assert( pItem->pSelect && (pItem->pSelect->selFlags & SF_PushDown)!=0 );
+      assert( pSubq->pSelect && (pSub->selFlags & SF_PushDown)!=0 );
     }else{
       TREETRACE(0x4000,pParse,p,("WHERE-lcause push-down not possible\n"));
     }
@@ -7752,17 +7806,17 @@ int sqlite3Select(
       */
       int addrTop = sqlite3VdbeCurrentAddr(v)+1;
     
-      pItem->regReturn = ++pParse->nMem;
-      sqlite3VdbeAddOp3(v, OP_InitCoroutine, pItem->regReturn, 0, addrTop);
+      pSubq->regReturn = ++pParse->nMem;
+      sqlite3VdbeAddOp3(v, OP_InitCoroutine, pSubq->regReturn, 0, addrTop);
       VdbeComment((v, "%!S", pItem));
-      pItem->addrFillSub = addrTop;
-      sqlite3SelectDestInit(&dest, SRT_Coroutine, pItem->regReturn);
+      pSubq->addrFillSub = addrTop;
+      sqlite3SelectDestInit(&dest, SRT_Coroutine, pSubq->regReturn);
       ExplainQueryPlan((pParse, 1, "CO-ROUTINE %!S", pItem));
       sqlite3Select(pParse, pSub, &dest);
-      pItem->pTab->nRowLogEst = pSub->nSelectRow;
+      pItem->pSTab->nRowLogEst = pSub->nSelectRow;
       pItem->fg.viaCoroutine = 1;
-      pItem->regResult = dest.iSdst;
-      sqlite3VdbeEndCoroutine(v, pItem->regReturn);
+      pSubq->regResult = dest.iSdst;
+      sqlite3VdbeEndCoroutine(v, pSubq->regReturn);
       sqlite3VdbeJumpHere(v, addrTop-1);
       sqlite3ClearTempRegCache(pParse);
     }else if( pItem->fg.isCte && pItem->u2.pCteUse->addrM9e>0 ){
@@ -7780,11 +7834,16 @@ int sqlite3Select(
     }else if( (pPrior = isSelfJoinView(pTabList, pItem, 0, i))!=0 ){
       /* This view has already been materialized by a prior entry in
       ** this same FROM clause.  Reuse it. */
-      if( pPrior->addrFillSub ){
-        sqlite3VdbeAddOp2(v, OP_Gosub, pPrior->regReturn, pPrior->addrFillSub);
+      Subquery *pPriorSubq;
+      assert( pPrior->fg.isSubquery );
+      pPriorSubq = pPrior->u4.pSubq;
+      assert( pPriorSubq!=0 );
+      if( pPriorSubq->addrFillSub ){
+        sqlite3VdbeAddOp2(v, OP_Gosub, pPriorSubq->regReturn,
+                                       pPriorSubq->addrFillSub);
       }
       sqlite3VdbeAddOp2(v, OP_OpenDup, pItem->iCursor, pPrior->iCursor);
-      pSub->nSelectRow = pPrior->pSelect->nSelectRow;
+      pSub->nSelectRow = pPriorSubq->pSelect->nSelectRow;
     }else{
       /* Materialize the view.  If the view is not correlated, generate a
       ** subroutine to do the materialization so that subsequent uses of
@@ -7795,9 +7854,9 @@ int sqlite3Select(
       int addrExplain;
 #endif
 
-      pItem->regReturn = ++pParse->nMem;
+      pSubq->regReturn = ++pParse->nMem;
       topAddr = sqlite3VdbeAddOp0(v, OP_Goto);
-      pItem->addrFillSub = topAddr+1;
+      pSubq->addrFillSub = topAddr+1;
       pItem->fg.isMaterialized = 1;
       if( pItem->fg.isCorrelated==0 ){
         /* If the subquery is not correlated and if we are not inside of
@@ -7812,17 +7871,17 @@ int sqlite3Select(
 
       ExplainQueryPlan2(addrExplain, (pParse, 1, "MATERIALIZE %!S", pItem));
       sqlite3Select(pParse, pSub, &dest);
-      pItem->pTab->nRowLogEst = pSub->nSelectRow;
+      pItem->pSTab->nRowLogEst = pSub->nSelectRow;
       if( onceAddr ) sqlite3VdbeJumpHere(v, onceAddr);
-      sqlite3VdbeAddOp2(v, OP_Return, pItem->regReturn, topAddr+1);
+      sqlite3VdbeAddOp2(v, OP_Return, pSubq->regReturn, topAddr+1);
       VdbeComment((v, "end %!S", pItem));
       sqlite3VdbeScanStatusRange(v, addrExplain, addrExplain, -1);
       sqlite3VdbeJumpHere(v, topAddr);
       sqlite3ClearTempRegCache(pParse);
       if( pItem->fg.isCte && pItem->fg.isCorrelated==0 ){
         CteUse *pCteUse = pItem->u2.pCteUse;
-        pCteUse->addrM9e = pItem->addrFillSub;
-        pCteUse->regRtn = pItem->regReturn;
+        pCteUse->addrM9e = pSubq->addrFillSub;
+        pCteUse->regRtn = pSubq->regReturn;
         pCteUse->iCur = pItem->iCursor;
         pCteUse->nRowEst = pSub->nSelectRow;
       }
diff --git a/src/sqliteInt.h b/src/sqliteInt.h
index ebd0f01b2..d1ffce6d8 100644
--- a/src/sqliteInt.h
+++ b/src/sqliteInt.h
@@ -1335,6 +1335,7 @@ typedef struct Savepoint Savepoint;
 typedef struct Select Select;
 typedef struct SQLiteThread SQLiteThread;
 typedef struct SelectDest SelectDest;
+typedef struct Subquery Subquery;
 typedef struct SrcItem SrcItem;
 typedef struct SrcList SrcList;
 typedef struct sqlite3_str StrAccum; /* Internal alias for sqlite3_str */
@@ -3276,6 +3277,16 @@ struct IdList {
 #define EU4_EXPR   2   /* Uses IdList.a.u4.pExpr -- NOT CURRENTLY USED */
 
 /*
+** Details of the implementation of a subquery.
+*/
+struct Subquery {
+  Select *pSelect;  /* A SELECT statement used in place of a table name */
+  int addrFillSub;  /* Address of subroutine to initialize a subquery */
+  int regReturn;    /* Register holding return address of addrFillSub */
+  int regResult;    /* Registers holding results of a co-routine */
+};
+
+/*
 ** The SrcItem object represents a single term in the FROM clause of a query.
 ** The SrcList object is mostly an array of SrcItems.
 **
@@ -3287,29 +3298,40 @@ struct IdList {
 ** In the colUsed field, the high-order bit (bit 63) is set if the table
 ** contains more than 63 columns and the 64-th or later column is used.
 **
-** Union member validity:
+** Aggressive use of "union" helps keep the size of the object small.  This
+** has been shown to boost performance, in addition to saving memory.
+** Access to union elements is gated by the following rules which should
+** always be checked, either by an if-statement or by an assert().
 **
-**    u1.zIndexedBy      fg.isIndexedBy && !fg.isTabFunc
-**    u1.pFuncArg        fg.isTabFunc   && !fg.isIndexedBy
+**    Field              Only access if this is true
+**    ---------------    -----------------------------------
+**    u1.zIndexedBy      fg.isIndexedBy
+**    u1.pFuncArg        fg.isTabFunc
 **    u1.nRow            !fg.isTabFunc  && !fg.isIndexedBy
 **
-**    u2.pIBIndex        fg.isIndexedBy && !fg.isCte
-**    u2.pCteUse         fg.isCte       && !fg.isIndexedBy
+**    u2.pIBIndex        fg.isIndexedBy
+**    u2.pCteUse         fg.isCte
+**
+**    u3.pOn             !fg.isUsing
+**    u3.pUsing          fg.isUsing
+**
+**    u4.zDatabase       !fg.fixedSchema && !fg.isSubquery
+**    u4.pSchema         fg.fixedSchema
+**    u4.pSubq           fg.isSubquery
+**
+** See also the sqlite3SrcListDelete() routine for assert() statements that
+** check invariants on the fields of this object, especially the flags
+** inside the fg struct.
 */
 struct SrcItem {
-  Schema *pSchema;  /* Schema to which this item is fixed */
-  char *zDatabase;  /* Name of database holding this table */
   char *zName;      /* Name of the table */
   char *zAlias;     /* The "B" part of a "A AS B" phrase.  zName is the "A" */
-  Table *pTab;      /* An SQL table corresponding to zName */
-  Select *pSelect;  /* A SELECT statement used in place of a table name */
-  int addrFillSub;  /* Address of subroutine to manifest a subquery */
-  int regReturn;    /* Register holding return address of addrFillSub */
-  int regResult;    /* Registers holding results of a co-routine */
+  Table *pSTab;     /* Table object for zName. Mnemonic: Srcitem-TABle */
   struct {
     u8 jointype;      /* Type of join between this table and the previous */
     unsigned notIndexed :1;    /* True if there is a NOT INDEXED clause */
     unsigned isIndexedBy :1;   /* True if there is an INDEXED BY clause */
+    unsigned isSubquery :1;    /* True if this term is a subquery */
     unsigned isTabFunc :1;     /* True if table-valued-function syntax */
     unsigned isCorrelated :1;  /* True if sub-query is correlated */
     unsigned isMaterialized:1; /* This is a materialized view */
@@ -3323,12 +3345,10 @@ struct SrcItem {
     unsigned isSynthUsing :1;  /* u3.pUsing is synthesized from NATURAL */
     unsigned isNestedFrom :1;  /* pSelect is a SF_NestedFrom subquery */
     unsigned rowidUsed :1;     /* The ROWID of this table is referenced */
+    unsigned fixedSchema :1;   /* Uses u4.pSchema, not u4.zDatabase */
+    unsigned hadSchema :1;     /* Had u4.zDatabase before u4.pSchema */
   } fg;
   int iCursor;      /* The VDBE cursor number used to access this table */
-  union {
-    Expr *pOn;        /* fg.isUsing==0 =>  The ON clause of a join */
-    IdList *pUsing;   /* fg.isUsing==1 =>  The USING clause of a join */
-  } u3;
   Bitmask colUsed;  /* Bit N set if column N used. Details above for N>62 */
   union {
     char *zIndexedBy;    /* Identifier from "INDEXED BY <zIndex>" clause */
@@ -3339,6 +3359,15 @@ struct SrcItem {
     Index *pIBIndex;  /* Index structure corresponding to u1.zIndexedBy */
     CteUse *pCteUse;  /* CTE Usage info when fg.isCte is true */
   } u2;
+  union {
+    Expr *pOn;        /* fg.isUsing==0 =>  The ON clause of a join */
+    IdList *pUsing;   /* fg.isUsing==1 =>  The USING clause of a join */
+  } u3;
+  union {
+    Schema *pSchema;  /* Schema to which this item is fixed */
+    char *zDatabase;  /* Name of database holding this table */
+    Subquery *pSubq;  /* Description of a subquery */
+  } u4;
 };
 
 /*
@@ -3598,8 +3627,10 @@ struct Select {
 #define SF_UpdateFrom   0x10000000 /* Query originates with UPDATE FROM */
 #define SF_Correlated   0x20000000 /* True if references the outer context */
 
-/* True if S exists and has SF_NestedFrom */
-#define IsNestedFrom(S) ((S)!=0 && ((S)->selFlags&SF_NestedFrom)!=0)
+/* True if SrcItem X is a subquery that has SF_NestedFrom */
+#define IsNestedFrom(X) \
+   ((X)->fg.isSubquery && \
+    ((X)->u4.pSubq->pSelect->selFlags&SF_NestedFrom)!=0)
 
 /*
 ** The results of a SELECT can be distributed in several ways, as defined
@@ -4991,6 +5022,9 @@ int sqlite3IdListIndex(IdList*,const char*);
 SrcList *sqlite3SrcListEnlarge(Parse*, SrcList*, int, int);
 SrcList *sqlite3SrcListAppendList(Parse *pParse, SrcList *p1, SrcList *p2);
 SrcList *sqlite3SrcListAppend(Parse*, SrcList*, Token*, Token*);
+void sqlite3SubqueryDelete(sqlite3*,Subquery*);
+Select *sqlite3SubqueryDetach(sqlite3*,SrcItem*);
+int sqlite3SrcItemAttachSubquery(Parse*, SrcItem*, Select*, int);
 SrcList *sqlite3SrcListAppendFromTerm(Parse*, SrcList*, Token*, Token*,
                                       Token*, Select*, OnOrUsing*);
 void sqlite3SrcListIndexedBy(Parse *, SrcList *, Token *);
diff --git a/src/treeview.c b/src/treeview.c
index 3960d2859..dbd54b346 100644
--- a/src/treeview.c
+++ b/src/treeview.c
@@ -193,9 +193,9 @@ void sqlite3TreeViewSrcList(TreeView *pView, const SrcList *pSrc){
     sqlite3StrAccumInit(&x, 0, zLine, sizeof(zLine), 0);
     x.printfFlags |= SQLITE_PRINTF_INTERNAL;
     sqlite3_str_appendf(&x, "{%d:*} %!S", pItem->iCursor, pItem);
-    if( pItem->pTab ){
+    if( pItem->pSTab ){
       sqlite3_str_appendf(&x, " tab=%Q nCol=%d ptr=%p used=%llx%s",
-           pItem->pTab->zName, pItem->pTab->nCol, pItem->pTab, 
+           pItem->pSTab->zName, pItem->pSTab->nCol, pItem->pSTab, 
            pItem->colUsed,
            pItem->fg.rowidUsed ? "+rowid" : "");
     }
@@ -230,19 +230,19 @@ void sqlite3TreeViewSrcList(TreeView *pView, const SrcList *pSrc){
     sqlite3StrAccumFinish(&x);
     sqlite3TreeViewItem(pView, zLine, i<pSrc->nSrc-1);
     n = 0;
-    if( pItem->pSelect ) n++;
+    if( pItem->fg.isSubquery ) n++;
     if( pItem->fg.isTabFunc ) n++;
     if( pItem->fg.isUsing ) n++;
     if( pItem->fg.isUsing ){
       sqlite3TreeViewIdList(pView, pItem->u3.pUsing, (--n)>0, "USING");
     }
-    if( pItem->pSelect ){
-      if( pItem->pTab ){
-        Table *pTab = pItem->pTab;
+    if( pItem->fg.isSubquery ){
+      if( pItem->pSTab ){
+        Table *pTab = pItem->pSTab;
         sqlite3TreeViewColumnList(pView, pTab->aCol, pTab->nCol, 1);
       }
-      assert( (int)pItem->fg.isNestedFrom == IsNestedFrom(pItem->pSelect) );
-      sqlite3TreeViewSelect(pView, pItem->pSelect, (--n)>0);
+      assert( (int)pItem->fg.isNestedFrom == IsNestedFrom(pItem) );
+      sqlite3TreeViewSelect(pView, pItem->u4.pSubq->pSelect, (--n)>0);
     }
     if( pItem->fg.isTabFunc ){
       sqlite3TreeViewExprList(pView, pItem->u1.pFuncArg, 0, "func-args:");
diff --git a/src/trigger.c b/src/trigger.c
index 98e8da58c..ff2df82cb 100644
--- a/src/trigger.c
+++ b/src/trigger.c
@@ -152,8 +152,10 @@ void sqlite3BeginTrigger(
   ** name on pTableName if we are reparsing out of the schema table
   */
   if( db->init.busy && iDb!=1 ){
-    sqlite3DbFree(db, pTableName->a[0].zDatabase);
-    pTableName->a[0].zDatabase = 0;
+    assert( pTableName->a[0].fg.fixedSchema==0 );
+    assert( pTableName->a[0].fg.isSubquery==0 );
+    sqlite3DbFree(db, pTableName->a[0].u4.zDatabase);
+    pTableName->a[0].u4.zDatabase = 0;
   }
 
   /* If the trigger name was unqualified, and the table is a temp table,
@@ -631,7 +633,8 @@ void sqlite3DropTrigger(Parse *pParse, SrcList *pName, int noErr){
   }
 
   assert( pName->nSrc==1 );
-  zDb = pName->a[0].zDatabase;
+  assert( pName->a[0].fg.fixedSchema==0 && pName->a[0].fg.isSubquery==0 );
+  zDb = pName->a[0].u4.zDatabase;
   zName = pName->a[0].zName;
   assert( zDb!=0 || sqlite3BtreeHoldsAllMutexes(db) );
   for(i=OMIT_TEMPDB; i<db->nDb; i++){
@@ -868,7 +871,9 @@ SrcList *sqlite3TriggerStepSrc(
     Schema *pSchema = pStep->pTrig->pSchema;
     pSrc->a[0].zName = zName;
     if( pSchema!=db->aDb[1].pSchema ){
-      pSrc->a[0].pSchema = pSchema;
+      assert( pSrc->a[0].fg.fixedSchema || pSrc->a[0].u4.zDatabase==0 );
+      pSrc->a[0].u4.pSchema = pSchema;
+      pSrc->a[0].fg.fixedSchema = 1;
     }
     if( pStep->pFrom ){
       SrcList *pDup = sqlite3SrcListDup(db, pStep->pFrom, 0);
@@ -981,7 +986,7 @@ static int sqlite3ReturningSubqueryCorrelated(Walker *pWalker, Select *pSelect){
   pSrc = pSelect->pSrc;
   assert( pSrc!=0 );
   for(i=0; i<pSrc->nSrc; i++){
-    if( pSrc->a[i].pTab==pWalker->u.pTab ){
+    if( pSrc->a[i].pSTab==pWalker->u.pTab ){
       testcase( pSelect->selFlags & SF_Correlated );
       pSelect->selFlags |= SF_Correlated;
       pWalker->eCode = 1;
@@ -1052,7 +1057,7 @@ static void codeReturningTrigger(
   sSelect.pEList = sqlite3ExprListDup(db, pReturning->pReturnEL, 0);
   sSelect.pSrc = &sFrom;
   sFrom.nSrc = 1;
-  sFrom.a[0].pTab = pTab;
+  sFrom.a[0].pSTab = pTab;
   sFrom.a[0].zName = pTab->zName; /* tag-20240424-1 */
   sFrom.a[0].iCursor = -1;
   sqlite3SelectPrep(pParse, &sSelect, 0);
diff --git a/src/update.c b/src/update.c
index b6068caa7..a8e7f7780 100644
--- a/src/update.c
+++ b/src/update.c
@@ -202,7 +202,7 @@ static void updateFromSelect(
   Expr *pLimit2 = 0;
   ExprList *pOrderBy2 = 0;
   sqlite3 *db = pParse->db;
-  Table *pTab = pTabList->a[0].pTab;
+  Table *pTab = pTabList->a[0].pSTab;
   SrcList *pSrc;
   Expr *pWhere2;
   int eDest;
@@ -226,8 +226,8 @@ static void updateFromSelect(
   if( pSrc ){
     assert( pSrc->a[0].fg.notCte );
     pSrc->a[0].iCursor = -1;
-    pSrc->a[0].pTab->nTabRef--;
-    pSrc->a[0].pTab = 0;
+    pSrc->a[0].pSTab->nTabRef--;
+    pSrc->a[0].pSTab = 0;
   }
   if( pPk ){
     for(i=0; i<pPk->nKeyCol; i++){
diff --git a/src/upsert.c b/src/upsert.c
index f74d4fabf..82295d52a 100644
--- a/src/upsert.c
+++ b/src/upsert.c
@@ -104,7 +104,7 @@ int sqlite3UpsertAnalyzeTarget(
   int nClause = 0;        /* Counter of ON CONFLICT clauses */
 
   assert( pTabList->nSrc==1 );
-  assert( pTabList->a[0].pTab!=0 );
+  assert( pTabList->a[0].pSTab!=0 );
   assert( pUpsert!=0 );
   assert( pUpsert->pUpsertTarget!=0 );
 
@@ -123,7 +123,7 @@ int sqlite3UpsertAnalyzeTarget(
     if( rc ) return rc;
   
     /* Check to see if the conflict target matches the rowid. */  
-    pTab = pTabList->a[0].pTab;
+    pTab = pTabList->a[0].pSTab;
     pTarget = pUpsert->pUpsertTarget;
     iCursor = pTabList->a[0].iCursor;
     if( HasRowid(pTab) 
diff --git a/src/walker.c b/src/walker.c
index 0fe4a1d37..c8735e39b 100644
--- a/src/walker.c
+++ b/src/walker.c
@@ -171,7 +171,9 @@ int sqlite3WalkSelectFrom(Walker *pWalker, Select *p){
   pSrc = p->pSrc;
   if( ALWAYS(pSrc) ){
     for(i=pSrc->nSrc, pItem=pSrc->a; i>0; i--, pItem++){
-      if( pItem->pSelect && sqlite3WalkSelect(pWalker, pItem->pSelect) ){
+      if( pItem->fg.isSubquery
+       && sqlite3WalkSelect(pWalker, pItem->u4.pSubq->pSelect)
+      ){
         return WRC_Abort;
       }
       if( pItem->fg.isTabFunc
diff --git a/src/where.c b/src/where.c
index 631b7581f..c9f6b97c9 100644
--- a/src/where.c
+++ b/src/where.c
@@ -644,7 +644,7 @@ static int isDistinctRedundant(
   ** clause is redundant. */
   if( pTabList->nSrc!=1 ) return 0;
   iBase = pTabList->a[0].iCursor;
-  pTab = pTabList->a[0].pTab;
+  pTab = pTabList->a[0].pSTab;
 
   /* If any of the expressions is an IPK column on table iBase, then return
   ** true. Note: The (p->iTable==iBase) part of this test may be false if the
@@ -908,10 +908,10 @@ static int termCanDriveIndex(
   assert( (pTerm->eOperator & (WO_OR|WO_AND))==0 );
   leftCol = pTerm->u.x.leftColumn;
   if( leftCol<0 ) return 0;
-  aff = pSrc->pTab->aCol[leftCol].affinity;
+  aff = pSrc->pSTab->aCol[leftCol].affinity;
   if( !sqlite3IndexAffinityOk(pTerm->pExpr, aff) ) return 0;
   testcase( pTerm->pExpr->op==TK_IS );
-  return columnIsGoodIndexCandidate(pSrc->pTab, leftCol);
+  return columnIsGoodIndexCandidate(pSrc->pSTab, leftCol);
 }
 #endif
 
@@ -1019,7 +1019,7 @@ static SQLITE_NOINLINE void constructAutomaticIndex(
   nKeyCol = 0;
   pTabList = pWC->pWInfo->pTabList;
   pSrc = &pTabList->a[pLevel->iFrom];
-  pTable = pSrc->pTab;
+  pTable = pSrc->pSTab;
   pWCEnd = &pWC->a[pWC->nTerm];
   pLoop = pLevel->pWLoop;
   idxCols = 0;
@@ -1161,12 +1161,17 @@ static SQLITE_NOINLINE void constructAutomaticIndex(
   /* Fill the automatic index with content */
   assert( pSrc == &pWC->pWInfo->pTabList->a[pLevel->iFrom] );
   if( pSrc->fg.viaCoroutine ){
-    int regYield = pSrc->regReturn;
+    int regYield;
+    Subquery *pSubq;
+    assert( pSrc->fg.isSubquery );
+    pSubq = pSrc->u4.pSubq;
+    assert( pSubq!=0 );
+    regYield = pSubq->regReturn;
     addrCounter = sqlite3VdbeAddOp2(v, OP_Integer, 0, 0);
-    sqlite3VdbeAddOp3(v, OP_InitCoroutine, regYield, 0, pSrc->addrFillSub);
+    sqlite3VdbeAddOp3(v, OP_InitCoroutine, regYield, 0, pSubq->addrFillSub);
     addrTop =  sqlite3VdbeAddOp1(v, OP_Yield, regYield);
     VdbeCoverage(v);
-    VdbeComment((v, "next row of %s", pSrc->pTab->zName));
+    VdbeComment((v, "next row of %s", pSrc->pSTab->zName));
   }else{
     addrTop = sqlite3VdbeAddOp1(v, OP_Rewind, pLevel->iTabCur); VdbeCoverage(v);
   }
@@ -1188,11 +1193,12 @@ static SQLITE_NOINLINE void constructAutomaticIndex(
   sqlite3VdbeChangeP5(v, OPFLAG_USESEEKRESULT);
   if( pPartial ) sqlite3VdbeResolveLabel(v, iContinue);
   if( pSrc->fg.viaCoroutine ){
+    assert( pSrc->fg.isSubquery && pSrc->u4.pSubq!=0 );
     sqlite3VdbeChangeP2(v, addrCounter, regBase+n);
     testcase( pParse->db->mallocFailed );
     assert( pLevel->iIdxCur>0 );
     translateColumnToCopy(pParse, addrTop, pLevel->iTabCur,
-                          pSrc->regResult, pLevel->iIdxCur);
+                          pSrc->u4.pSubq->regResult, pLevel->iIdxCur);
     sqlite3VdbeGoto(v, addrTop);
     pSrc->fg.viaCoroutine = 0;
   }else{
@@ -1283,7 +1289,7 @@ static SQLITE_NOINLINE void sqlite3ConstructBloomFilter(
     iSrc = pLevel->iFrom;
     pItem = &pTabList->a[iSrc];
     assert( pItem!=0 );
-    pTab = pItem->pTab;
+    pTab = pItem->pSTab;
     assert( pTab!=0 );
     sz = sqlite3LogEstToInt(pTab->nRowLogEst);
     if( sz<10000 ){
@@ -1314,7 +1320,7 @@ static SQLITE_NOINLINE void sqlite3ConstructBloomFilter(
       int r1 = sqlite3GetTempRange(pParse, n);
       int jj;
       for(jj=0; jj<n; jj++){
-        assert( pIdx->pTable==pItem->pTab );
+        assert( pIdx->pTable==pItem->pSTab );
         sqlite3ExprCodeLoadIndexColumn(pParse, pIdx, iCur, jj, r1+jj);
       }
       sqlite3VdbeAddOp4Int(v, OP_FilterAdd, pLevel->regFilter, 0, r1, n);
@@ -1395,7 +1401,7 @@ static sqlite3_index_info *allocateIndexInfo(
   WhereClause *p;
 
   assert( pSrc!=0 );
-  pTab = pSrc->pTab;
+  pTab = pSrc->pSTab;
   assert( pTab!=0 );
   assert( IsVirtual(pTab) );
 
@@ -2403,7 +2409,7 @@ void sqlite3WhereLoopPrint(const WhereLoop *p, const WhereClause *pWC){
     WhereInfo *pWInfo = pWC->pWInfo;
     int nb = 1+(pWInfo->pTabList->nSrc+3)/4;
     SrcItem *pItem = pWInfo->pTabList->a + p->iTab;
-    Table *pTab = pItem->pTab;
+    Table *pTab = pItem->pSTab;
     Bitmask mAll = (((Bitmask)1)<<(nb*4)) - 1;
     sqlite3DebugPrintf("%c%2d.%0*llx.%0*llx", p->cId,
                        p->iTab, nb, p->maskSelf, nb, p->prereq & mAll);
@@ -3391,7 +3397,7 @@ static int whereLoopAddBtreeIndex(
     **   2.  Stepping forward in the index pNew->nOut times to find all
     **       additional matching entries.
     */
-    assert( pSrc->pTab->szTabRow>0 );
+    assert( pSrc->pSTab->szTabRow>0 );
     if( pProbe->idxType==SQLITE_IDXTYPE_IPK ){
       /* The pProbe->szIdxRow is low for an IPK table since the interior
       ** pages are small.  Thus szIdxRow gives a good estimate of seek cost.
@@ -3399,7 +3405,7 @@ static int whereLoopAddBtreeIndex(
       ** under-estimate the scanning cost. */
       rCostIdx = pNew->nOut + 16;
     }else{
-      rCostIdx = pNew->nOut + 1 + (15*pProbe->szIdxRow)/pSrc->pTab->szTabRow;
+      rCostIdx = pNew->nOut + 1 + (15*pProbe->szIdxRow)/pSrc->pSTab->szTabRow;
     }
     rCostIdx = sqlite3LogEstAdd(rLogSize, rCostIdx);
 
@@ -3864,9 +3870,9 @@ static int whereLoopAddBtree(
   pWInfo = pBuilder->pWInfo;
   pTabList = pWInfo->pTabList;
   pSrc = pTabList->a + pNew->iTab;
-  pTab = pSrc->pTab;
+  pTab = pSrc->pSTab;
   pWC = pBuilder->pWC;
-  assert( !IsVirtual(pSrc->pTab) );
+  assert( !IsVirtual(pSrc->pSTab) );
 
   if( pSrc->fg.isIndexedBy ){
     assert( pSrc->fg.isCte==0 );
@@ -3891,7 +3897,7 @@ static int whereLoopAddBtree(
     sPk.idxType = SQLITE_IDXTYPE_IPK;
     aiRowEstPk[0] = pTab->nRowLogEst;
     aiRowEstPk[1] = 0;
-    pFirst = pSrc->pTab->pIndex;
+    pFirst = pSrc->pSTab->pIndex;
     if( pSrc->fg.notIndexed==0 ){
       /* The real indices of the table are only considered if the
       ** NOT INDEXED qualifier is omitted from the FROM clause */
@@ -4010,9 +4016,9 @@ static int whereLoopAddBtree(
 #endif
       ApplyCostMultiplier(pNew->rRun, pTab->costMult);
       whereLoopOutputAdjust(pWC, pNew, rSize);
-      if( pSrc->pSelect ){
+      if( pSrc->fg.isSubquery ){
         if( pSrc->fg.viaCoroutine ) pNew->wsFlags |= WHERE_COROUTINE;
-        pNew->u.btree.pOrderBy = pSrc->pSelect->pOrderBy;
+        pNew->u.btree.pOrderBy = pSrc->u4.pSubq->pSelect->pOrderBy;
       }
       rc = whereLoopInsert(pBuilder, pNew);
       pNew->nOut = rSize;
@@ -4238,7 +4244,7 @@ static int whereLoopAddVirtualOne(
   pHidden->mHandleIn = 0;
 
   /* Invoke the virtual table xBestIndex() method */
-  rc = vtabBestIndex(pParse, pSrc->pTab, pIdxInfo);
+  rc = vtabBestIndex(pParse, pSrc->pSTab, pIdxInfo);
   if( rc ){
     if( rc==SQLITE_CONSTRAINT ){
       /* If the xBestIndex method returns SQLITE_CONSTRAINT, that means
@@ -4268,7 +4274,7 @@ static int whereLoopAddVirtualOne(
        || pNew->aLTerm[iTerm]!=0
        || pIdxCons->usable==0
       ){
-        sqlite3ErrorMsg(pParse,"%s.xBestIndex malfunction",pSrc->pTab->zName);
+        sqlite3ErrorMsg(pParse,"%s.xBestIndex malfunction",pSrc->pSTab->zName);
         freeIdxStr(pIdxInfo);
         return SQLITE_ERROR;
       }
@@ -4331,7 +4337,7 @@ static int whereLoopAddVirtualOne(
     if( pNew->aLTerm[i]==0 ){
       /* The non-zero argvIdx values must be contiguous.  Raise an
       ** error if they are not */
-      sqlite3ErrorMsg(pParse,"%s.xBestIndex malfunction",pSrc->pTab->zName);
+      sqlite3ErrorMsg(pParse,"%s.xBestIndex malfunction",pSrc->pSTab->zName);
       freeIdxStr(pIdxInfo);
       return SQLITE_ERROR;
     }
@@ -4533,7 +4539,7 @@ static int whereLoopAddVirtual(
   pWC = pBuilder->pWC;
   pNew = pBuilder->pNew;
   pSrc = &pWInfo->pTabList->a[pNew->iTab];
-  assert( IsVirtual(pSrc->pTab) );
+  assert( IsVirtual(pSrc->pSTab) );
   p = allocateIndexInfo(pWInfo, pWC, mUnusable, pSrc, &mNoOmit);
   if( p==0 ) return SQLITE_NOMEM_BKPT;
   pNew->rSetup = 0;
@@ -4547,7 +4553,7 @@ static int whereLoopAddVirtual(
   }
 
   /* First call xBestIndex() with all constraints usable. */
-  WHERETRACE(0x800, ("BEGIN %s.addVirtual()\n", pSrc->pTab->zName));
+  WHERETRACE(0x800, ("BEGIN %s.addVirtual()\n", pSrc->pSTab->zName));
   WHERETRACE(0x800, ("  VirtualOne: all usable\n"));
   rc = whereLoopAddVirtualOne(
       pBuilder, mPrereq, ALLBITS, 0, p, mNoOmit, &bIn, &bRetry
@@ -4629,7 +4635,7 @@ static int whereLoopAddVirtual(
   }
 
   freeIndexInfo(pParse->db, p);
-  WHERETRACE(0x800, ("END %s.addVirtual(), rc=%d\n", pSrc->pTab->zName, rc));
+  WHERETRACE(0x800, ("END %s.addVirtual(), rc=%d\n", pSrc->pSTab->zName, rc));
   return rc;
 }
 #endif /* SQLITE_OMIT_VIRTUALTABLE */
@@ -4701,7 +4707,7 @@ static int whereLoopAddOr(
         }
 #endif
 #ifndef SQLITE_OMIT_VIRTUALTABLE
-        if( IsVirtual(pItem->pTab) ){
+        if( IsVirtual(pItem->pSTab) ){
           rc = whereLoopAddVirtual(&sSubBuild, mPrereq, mUnusable);
         }else
 #endif
@@ -4815,7 +4821,7 @@ static int whereLoopAddAll(WhereLoopBuilder *pBuilder){
       mPrereq = 0;
     }
 #ifndef SQLITE_OMIT_VIRTUALTABLE
-    if( IsVirtual(pItem->pTab) ){
+    if( IsVirtual(pItem->pSTab) ){
       SrcItem *p;
       for(p=&pItem[1]; p<pEnd; p++){
         if( mUnusable || (p->fg.jointype & (JT_OUTER|JT_CROSS)) ){
@@ -5451,7 +5457,7 @@ static int computeMxChoice(WhereInfo *pWInfo, LogEst nRowEst){
       if( sqlite3WhereTrace&0x4 ){
          SrcItem *pItem = pWInfo->pTabList->a + iLoop;
          sqlite3DebugPrintf("Fact-table %s: %d dimensions, cost reduced %d\n",
-             pItem->zAlias ? pItem->zAlias : pItem->pTab->zName,
+             pItem->zAlias ? pItem->zAlias : pItem->pSTab->zName,
              nDep, rDelta);
       }
 #endif
@@ -6001,7 +6007,7 @@ static int whereShortCut(WhereLoopBuilder *pBuilder){
   if( pWInfo->wctrlFlags & WHERE_OR_SUBCLAUSE ) return 0;
   assert( pWInfo->pTabList->nSrc>=1 );
   pItem = pWInfo->pTabList->a;
-  pTab = pItem->pTab;
+  pTab = pItem->pSTab;
   if( IsVirtual(pTab) ) return 0;
   if( pItem->fg.isIndexedBy || pItem->fg.notIndexed ){
     testcase( pItem->fg.isIndexedBy );
@@ -6264,7 +6270,7 @@ static SQLITE_NOINLINE void whereCheckIfBloomFilterIsUseful(
     WhereLoop *pLoop = pWInfo->a[i].pWLoop;
     const unsigned int reqFlags = (WHERE_SELFCULL|WHERE_COLUMN_EQ);
     SrcItem *pItem = &pWInfo->pTabList->a[pLoop->iTab];
-    Table *pTab = pItem->pTab;
+    Table *pTab = pItem->pSTab;
     if( (pTab->tabFlags & TF_HasStat1)==0 ) break;
     pTab->tabFlags |= TF_MaybeReanalyze;
     if( i>=1
@@ -6421,8 +6427,8 @@ static SQLITE_NOINLINE void whereReverseScanOrder(WhereInfo *pWInfo){
     SrcItem *pItem = &pWInfo->pTabList->a[ii];
     if( !pItem->fg.isCte
      || pItem->u2.pCteUse->eM10d!=M10d_Yes
-     || NEVER(pItem->pSelect==0)
-     || pItem->pSelect->pOrderBy==0
+     || NEVER(pItem->fg.isSubquery==0)
+     || pItem->u4.pSubq->pSelect->pOrderBy==0
     ){
       pWInfo->revMask |= MASKBIT(ii);
     }
@@ -6912,15 +6918,15 @@ WhereInfo *sqlite3WhereBegin(
   if( (wctrlFlags & WHERE_ONEPASS_DESIRED)!=0 ){
     int wsFlags = pWInfo->a[0].pWLoop->wsFlags;
     int bOnerow = (wsFlags & WHERE_ONEROW)!=0;
-    assert( !(wsFlags & WHERE_VIRTUALTABLE) || IsVirtual(pTabList->a[0].pTab) );
+    assert( !(wsFlags&WHERE_VIRTUALTABLE) || IsVirtual(pTabList->a[0].pSTab) );
     if( bOnerow || (
         0!=(wctrlFlags & WHERE_ONEPASS_MULTIROW)
-     && !IsVirtual(pTabList->a[0].pTab)
+     && !IsVirtual(pTabList->a[0].pSTab)
      && (0==(wsFlags & WHERE_MULTI_OR) || (wctrlFlags & WHERE_DUPLICATES_OK))
      && OptimizationEnabled(db, SQLITE_OnePass)
     )){
       pWInfo->eOnePass = bOnerow ? ONEPASS_SINGLE : ONEPASS_MULTI;
-      if( HasRowid(pTabList->a[0].pTab) && (wsFlags & WHERE_IDX_ONLY) ){
+      if( HasRowid(pTabList->a[0].pSTab) && (wsFlags & WHERE_IDX_ONLY) ){
         if( wctrlFlags & WHERE_ONEPASS_MULTIROW ){
           bFordelete = OPFLAG_FORDELETE;
         }
@@ -6938,7 +6944,7 @@ WhereInfo *sqlite3WhereBegin(
     SrcItem *pTabItem;
 
     pTabItem = &pTabList->a[pLevel->iFrom];
-    pTab = pTabItem->pTab;
+    pTab = pTabItem->pSTab;
     iDb = sqlite3SchemaToIndex(db, pTab->pSchema);
     pLoop = pLevel->pWLoop;
     if( (pTab->tabFlags & TF_Ephemeral)!=0 || IsView(pTab) ){
@@ -7009,7 +7015,7 @@ WhereInfo *sqlite3WhereBegin(
         iIndexCur = pLevel->iTabCur;
         op = 0;
       }else if( pWInfo->eOnePass!=ONEPASS_OFF ){
-        Index *pJ = pTabItem->pTab->pIndex;
+        Index *pJ = pTabItem->pSTab->pIndex;
         iIndexCur = iAuxArg;
         assert( wctrlFlags & WHERE_ONEPASS_DESIRED );
         while( ALWAYS(pJ) && pJ!=pIx ){
@@ -7076,7 +7082,7 @@ WhereInfo *sqlite3WhereBegin(
       sqlite3VdbeAddOp2(v, OP_Blob, 65536, pRJ->regBloom);
       pRJ->regReturn = ++pParse->nMem;
       sqlite3VdbeAddOp2(v, OP_Null, 0, pRJ->regReturn);
-      assert( pTab==pTabItem->pTab );
+      assert( pTab==pTabItem->pSTab );
       if( HasRowid(pTab) ){
         KeyInfo *pInfo;
         sqlite3VdbeAddOp2(v, OP_OpenEphemeral, pRJ->iMatch, 1);
@@ -7115,11 +7121,14 @@ WhereInfo *sqlite3WhereBegin(
     wsFlags = pLevel->pWLoop->wsFlags;
     pSrc = &pTabList->a[pLevel->iFrom];
     if( pSrc->fg.isMaterialized ){
+      Subquery *pSubq;
+      assert( pSrc->fg.isSubquery );
+      pSubq = pSrc->u4.pSubq;
       if( pSrc->fg.isCorrelated ){
-        sqlite3VdbeAddOp2(v, OP_Gosub, pSrc->regReturn, pSrc->addrFillSub);
+        sqlite3VdbeAddOp2(v, OP_Gosub, pSubq->regReturn, pSubq->addrFillSub);
       }else{
         int iOnce = sqlite3VdbeAddOp0(v, OP_Once);  VdbeCoverage(v);
-        sqlite3VdbeAddOp2(v, OP_Gosub, pSrc->regReturn, pSrc->addrFillSub);
+        sqlite3VdbeAddOp2(v, OP_Gosub, pSubq->regReturn, pSubq->addrFillSub);
         sqlite3VdbeJumpHere(v, iOnce);
       }
     }
@@ -7334,9 +7343,10 @@ void sqlite3WhereEnd(WhereInfo *pWInfo){
         assert( pLevel->iTabCur==pSrc->iCursor );
         if( pSrc->fg.viaCoroutine ){
           int m, n;
-          n = pSrc->regResult;
-          assert( pSrc->pTab!=0 );
-          m = pSrc->pTab->nCol;
+          assert( pSrc->fg.isSubquery );
+          n = pSrc->u4.pSubq->regResult;
+          assert( pSrc->pSTab!=0 );
+          m = pSrc->pSTab->nCol;
           sqlite3VdbeAddOp3(v, OP_Null, 0, n, n+m-1);
         }
         sqlite3VdbeAddOp1(v, OP_NullRow, pLevel->iTabCur);
@@ -7360,7 +7370,7 @@ void sqlite3WhereEnd(WhereInfo *pWInfo){
       sqlite3VdbeJumpHere(v, addr);
     }
     VdbeModuleComment((v, "End WHERE-loop%d: %s", i,
-                     pWInfo->pTabList->a[pLevel->iFrom].pTab->zName));
+                     pWInfo->pTabList->a[pLevel->iFrom].pSTab->zName));
   }
 
   assert( pWInfo->nLevel<=pTabList->nSrc );
@@ -7369,7 +7379,7 @@ void sqlite3WhereEnd(WhereInfo *pWInfo){
     VdbeOp *pOp, *pLastOp;
     Index *pIdx = 0;
     SrcItem *pTabItem = &pTabList->a[pLevel->iFrom];
-    Table *pTab = pTabItem->pTab;
+    Table *pTab = pTabItem->pSTab;
     assert( pTab!=0 );
     pLoop = pLevel->pWLoop;
 
@@ -7388,9 +7398,10 @@ void sqlite3WhereEnd(WhereInfo *pWInfo){
     */
     if( pTabItem->fg.viaCoroutine ){
       testcase( pParse->db->mallocFailed );
-      assert( pTabItem->regResult>=0 );
+      assert( pTabItem->fg.isSubquery );
+      assert( pTabItem->u4.pSubq->regResult>=0 );
       translateColumnToCopy(pParse, pLevel->addrBody, pLevel->iTabCur,
-                            pTabItem->regResult, 0);
+                            pTabItem->u4.pSubq->regResult, 0);
       continue;
     }
 
diff --git a/src/wherecode.c b/src/wherecode.c
index 098af7375..b0c0d9aed 100644
--- a/src/wherecode.c
+++ b/src/wherecode.c
@@ -157,7 +157,7 @@ int sqlite3WhereExplainOneScan(
       assert( pLoop->u.btree.pIndex!=0 );
       pIdx = pLoop->u.btree.pIndex;
       assert( !(flags&WHERE_AUTO_INDEX) || (flags&WHERE_IDX_ONLY) );
-      if( !HasRowid(pItem->pTab) && IsPrimaryKeyIndex(pIdx) ){
+      if( !HasRowid(pItem->pSTab) && IsPrimaryKeyIndex(pIdx) ){
         if( isSearch ){
           zFmt = "PRIMARY KEY";
         }
@@ -254,7 +254,7 @@ int sqlite3WhereExplainBloomFilter(
   sqlite3_str_appendf(&str, "BLOOM FILTER ON %S (", pItem);
   pLoop = pLevel->pWLoop;
   if( pLoop->wsFlags & WHERE_IPK ){
-    const Table *pTab = pItem->pTab;
+    const Table *pTab = pItem->pSTab;
     if( pTab->iPKey>=0 ){
       sqlite3_str_appendf(&str, "%s=?", pTab->aCol[pTab->iPKey].zCnName);
     }else{
@@ -317,7 +317,9 @@ void sqlite3WhereAddScanStatus(
         sqlite3VdbeScanStatusRange(v, addrExplain, -1, pLvl->iIdxCur);
       }
     }else{
-      int addr = pSrclist->a[pLvl->iFrom].addrFillSub;
+      int addr;
+      assert( pSrclist->a[pLvl->iFrom].fg.isSubquery );
+      addr = pSrclist->a[pLvl->iFrom].u4.pSubq->addrFillSub;
       VdbeOp *pOp = sqlite3VdbeGetOp(v, addr-1);
       assert( sqlite3VdbeDb(v)->mallocFailed || pOp->opcode==OP_InitCoroutine );
       assert( sqlite3VdbeDb(v)->mallocFailed || pOp->p2>addr );
@@ -1454,7 +1456,8 @@ Bitmask sqlite3WhereCodeOneLoopStart(
   iCur = pTabItem->iCursor;
   pLevel->notReady = notReady & ~sqlite3WhereGetMask(&pWInfo->sMaskSet, iCur);
   bRev = (pWInfo->revMask>>iLevel)&1;
-  VdbeModuleComment((v, "Begin WHERE-loop%d: %s",iLevel,pTabItem->pTab->zName));
+  VdbeModuleComment((v, "Begin WHERE-loop%d: %s",
+                     iLevel, pTabItem->pSTab->zName));
 #if WHERETRACE_ENABLED /* 0x4001 */
   if( sqlite3WhereTrace & 0x1 ){
     sqlite3DebugPrintf("Coding level %d of %d:  notReady=%llx  iFrom=%d\n",
@@ -1509,11 +1512,15 @@ Bitmask sqlite3WhereCodeOneLoopStart(
 
   /* Special case of a FROM clause subquery implemented as a co-routine */
   if( pTabItem->fg.viaCoroutine ){
-    int regYield = pTabItem->regReturn;
-    sqlite3VdbeAddOp3(v, OP_InitCoroutine, regYield, 0, pTabItem->addrFillSub);
+    int regYield;
+    Subquery *pSubq;
+    assert( pTabItem->fg.isSubquery && pTabItem->u4.pSubq!=0 );
+    pSubq = pTabItem->u4.pSubq;
+    regYield = pSubq->regReturn;
+    sqlite3VdbeAddOp3(v, OP_InitCoroutine, regYield, 0, pSubq->addrFillSub);
     pLevel->p2 =  sqlite3VdbeAddOp2(v, OP_Yield, regYield, addrBrk);
     VdbeCoverage(v);
-    VdbeComment((v, "next row of %s", pTabItem->pTab->zName));
+    VdbeComment((v, "next row of %s", pTabItem->pSTab->zName));
     pLevel->op = OP_Goto;
   }else
 
@@ -2242,7 +2249,7 @@ Bitmask sqlite3WhereCodeOneLoopStart(
     int untestedTerms = 0;             /* Some terms not completely tested */
     int ii;                            /* Loop counter */
     Expr *pAndExpr = 0;                /* An ".. AND (...)" expression */
-    Table *pTab = pTabItem->pTab;
+    Table *pTab = pTabItem->pSTab;
 
     pTerm = pLoop->aLTerm[0];
     assert( pTerm!=0 );
@@ -2701,7 +2708,7 @@ Bitmask sqlite3WhereCodeOneLoopStart(
     ** least once.  This is accomplished by storing the PK for the row in
     ** both the iMatch index and the regBloom Bloom filter.
     */
-    pTab = pWInfo->pTabList->a[pLevel->iFrom].pTab;
+    pTab = pWInfo->pTabList->a[pLevel->iFrom].pSTab;
     if( HasRowid(pTab) ){
       r = sqlite3GetTempRange(pParse, 2);
       sqlite3ExprCodeGetColumnOfTable(v, pTab, pLevel->iTabCur, -1, r+1);
@@ -2808,7 +2815,7 @@ SQLITE_NOINLINE void sqlite3WhereRightJoinLoop(
   Bitmask mAll = 0;
   int k;
 
-  ExplainQueryPlan((pParse, 1, "RIGHT-JOIN %s", pTabItem->pTab->zName));
+  ExplainQueryPlan((pParse, 1, "RIGHT-JOIN %s", pTabItem->pSTab->zName));
   sqlite3VdbeNoJumpsOutsideSubrtn(v, pRJ->addrSubrtn, pRJ->endSubrtn,
                                   pRJ->regReturn);
   for(k=0; k<iLevel; k++){
@@ -2818,9 +2825,13 @@ SQLITE_NOINLINE void sqlite3WhereRightJoinLoop(
     pRight = &pWInfo->pTabList->a[pWInfo->a[k].iFrom];
     mAll |= pWInfo->a[k].pWLoop->maskSelf;
     if( pRight->fg.viaCoroutine ){
+      Subquery *pSubq;
+      assert( pRight->fg.isSubquery && pRight->u4.pSubq!=0 );
+      pSubq = pRight->u4.pSubq;
+      assert( pSubq->pSelect!=0 && pSubq->pSelect->pEList!=0 );
       sqlite3VdbeAddOp3(
-          v, OP_Null, 0, pRight->regResult, 
-          pRight->regResult + pRight->pSelect->pEList->nExpr-1
+          v, OP_Null, 0, pSubq->regResult, 
+          pSubq->regResult + pSubq->pSelect->pEList->nExpr-1
       );
     }
     sqlite3VdbeAddOp1(v, OP_NullRow, pWInfo->a[k].iTabCur);
@@ -2858,7 +2869,7 @@ SQLITE_NOINLINE void sqlite3WhereRightJoinLoop(
     int nPk;
     int jmp;
     int addrCont = sqlite3WhereContinueLabel(pSubWInfo);
-    Table *pTab = pTabItem->pTab;
+    Table *pTab = pTabItem->pSTab;
     if( HasRowid(pTab) ){
       sqlite3ExprCodeGetColumnOfTable(v, pTab, iCur, -1, r);
       nPk = 1;
diff --git a/src/whereexpr.c b/src/whereexpr.c
index d44085a78..7ea2956a7 100644
--- a/src/whereexpr.c
+++ b/src/whereexpr.c
@@ -967,7 +967,9 @@ static Bitmask exprSelectUsage(WhereMaskSet *pMaskSet, Select *pS){
     if( ALWAYS(pSrc!=0) ){
       int i;
       for(i=0; i<pSrc->nSrc; i++){
-        mask |= exprSelectUsage(pMaskSet, pSrc->a[i].pSelect);
+        if( pSrc->a[i].fg.isSubquery ){
+          mask |= exprSelectUsage(pMaskSet, pSrc->a[i].u4.pSubq->pSelect);
+        }
         if( pSrc->a[i].fg.isUsing==0 ){
           mask |= sqlite3WhereExprUsage(pMaskSet, pSrc->a[i].u3.pOn);
         }
@@ -1005,7 +1007,7 @@ static SQLITE_NOINLINE int exprMightBeIndexed2(
   int iCur;
   do{
     iCur = pFrom->a[j].iCursor;
-    for(pIdx=pFrom->a[j].pTab->pIndex; pIdx; pIdx=pIdx->pNext){
+    for(pIdx=pFrom->a[j].pSTab->pIndex; pIdx; pIdx=pIdx->pNext){
       if( pIdx->aColExpr==0 ) continue;
       for(i=0; i<pIdx->nKeyCol; i++){
         if( pIdx->aiColumn[i]!=XN_EXPR ) continue;
@@ -1049,7 +1051,7 @@ static int exprMightBeIndexed(
 
   for(i=0; i<pFrom->nSrc; i++){
     Index *pIdx;
-    for(pIdx=pFrom->a[i].pTab->pIndex; pIdx; pIdx=pIdx->pNext){
+    for(pIdx=pFrom->a[i].pSTab->pIndex; pIdx; pIdx=pIdx->pNext){
       if( pIdx->aColExpr ){
         return exprMightBeIndexed2(pFrom,aiCurCol,pExpr,i);
       }
@@ -1637,7 +1639,7 @@ void SQLITE_NOINLINE sqlite3WhereAddLimit(WhereClause *pWC, Select *p){
   assert( p!=0 && p->pLimit!=0 );                 /* 1 -- checked by caller */
   if( p->pGroupBy==0
    && (p->selFlags & (SF_Distinct|SF_Aggregate))==0             /* 2 */
-   && (p->pSrc->nSrc==1 && IsVirtual(p->pSrc->a[0].pTab))       /* 3 */
+   && (p->pSrc->nSrc==1 && IsVirtual(p->pSrc->a[0].pSTab))      /* 3 */
   ){
     ExprList *pOrderBy = p->pOrderBy;
     int iCsr = p->pSrc->a[0].iCursor;
@@ -1858,7 +1860,7 @@ void sqlite3WhereTabFuncArgs(
   Expr *pColRef;
   Expr *pTerm;
   if( pItem->fg.isTabFunc==0 ) return;
-  pTab = pItem->pTab;
+  pTab = pItem->pSTab;
   assert( pTab!=0 );
   pArgs = pItem->u1.pFuncArg;
   if( pArgs==0 ) return;
diff --git a/src/window.c b/src/window.c
index e5a78e37d..d4083beeb 100644
--- a/src/window.c
+++ b/src/window.c
@@ -1077,9 +1077,10 @@ int sqlite3WindowRewrite(Parse *pParse, Select *p){
     assert( pSub!=0 || p->pSrc==0 ); /* Due to db->mallocFailed test inside
                                      ** of sqlite3DbMallocRawNN() called from
                                      ** sqlite3SrcListAppend() */
-    if( p->pSrc ){
+    if( p->pSrc==0 ){
+      sqlite3SelectDelete(db, pSub);
+    }else if( sqlite3SrcItemAttachSubquery(pParse, &p->pSrc->a[0], pSub, 0) ){
       Table *pTab2;
-      p->pSrc->a[0].pSelect = pSub;
       p->pSrc->a[0].fg.isCorrelated = 1;
       sqlite3SrcListAssignCursors(pParse, p->pSrc);
       pSub->selFlags |= SF_Expanded|SF_OrderByReqd;
@@ -1093,7 +1094,7 @@ int sqlite3WindowRewrite(Parse *pParse, Select *p){
       }else{
         memcpy(pTab, pTab2, sizeof(Table));
         pTab->tabFlags |= TF_Ephemeral;
-        p->pSrc->a[0].pTab = pTab;
+        p->pSrc->a[0].pSTab = pTab;
         pTab = pTab2;
         memset(&w, 0, sizeof(w));
         w.xExprCallback = sqlite3WindowExtraAggFuncDepth;
@@ -1101,8 +1102,6 @@ int sqlite3WindowRewrite(Parse *pParse, Select *p){
         w.xSelectCallback2 = sqlite3WalkerDepthDecrease;
         sqlite3WalkSelect(&w, pSub);
       }
-    }else{
-      sqlite3SelectDelete(db, pSub);
     }
     if( db->mallocFailed ) rc = SQLITE_NOMEM;
 
@@ -1389,10 +1388,15 @@ int sqlite3WindowCompare(
 ** and initialize registers and cursors used by sqlite3WindowCodeStep().
 */
 void sqlite3WindowCodeInit(Parse *pParse, Select *pSelect){
-  int nEphExpr = pSelect->pSrc->a[0].pSelect->pEList->nExpr;
-  Window *pMWin = pSelect->pWin;
   Window *pWin;
-  Vdbe *v = sqlite3GetVdbe(pParse);
+  int nEphExpr;
+  Window *pMWin;
+  Vdbe *v;
+
+  assert( pSelect->pSrc->a[0].fg.isSubquery );
+  nEphExpr = pSelect->pSrc->a[0].u4.pSubq->pSelect->pEList->nExpr;
+  pMWin = pSelect->pWin;
+  v = sqlite3GetVdbe(pParse);
 
   sqlite3VdbeAddOp2(v, OP_OpenEphemeral, pMWin->iEphCsr, nEphExpr);
   sqlite3VdbeAddOp2(v, OP_OpenDup, pMWin->iEphCsr+1, pMWin->iEphCsr);
@@ -2789,7 +2793,7 @@ void sqlite3WindowCodeStep(
   Vdbe *v = sqlite3GetVdbe(pParse);
   int csrWrite;                   /* Cursor used to write to eph. table */
   int csrInput = p->pSrc->a[0].iCursor;     /* Cursor of sub-select */
-  int nInput = p->pSrc->a[0].pTab->nCol;    /* Number of cols returned by sub */
+  int nInput = p->pSrc->a[0].pSTab->nCol;   /* Number of cols returned by sub */
   int iInput;                               /* To iterate through sub cols */
   int addrNe;                     /* Address of OP_Ne */
   int addrGosubFlush = 0;         /* Address of OP_Gosub to flush: */
diff --git a/test/with2.test b/test/with2.test
index 660df52b7..68790fe86 100644
--- a/test/with2.test
+++ b/test/with2.test
@@ -156,6 +156,16 @@ do_execsql_test 1.15 {
   SELECT * FROM t4;
 } {4 5}
 
+do_execsql_test 1.15.2 {
+  WITH 
+  t4(x) AS ( 
+    VALUES(4)
+    UNION ALL 
+    SELECT x+1 FROM (SELECT * FROM main.t4) WHERE x<10
+  )
+  SELECT * FROM t4;
+} {4 5}
+
 do_catchsql_test 1.16 {
   WITH 
   t4(x) AS (
author	drh <>	2024-08-20 23:11:28 +0000
committer	drh <>	2024-08-20 23:11:28 +0000
commit	5648d717b15c1722ff19e7af1e55d68d1d172f1d (patch)
tree	971f2c19f00ab2073124d4ecedaa7df3f0b42509
parent	781163aa9dce91608ba33af479564f83dda1bd40 (diff)
parent	a0651b370706e58f9014453c5f36124ca8a738c9 (diff)
download	sqlite-5648d717b15c1722ff19e7af1e55d68d1d172f1d.tar.gz sqlite-5648d717b15c1722ff19e7af1e55d68d1d172f1d.zip