Slight simplification to the query optimizer logic associated with IN (SELECT).

FossilOrigin-Name: 2c55c3c2950cafdc256ab540f60dc4609b9c354b

1 files changed, 15 insertions, 19 deletions

diff --git a/src/expr.c b/src/expr.c
index 22ca21de0..3672d02df 100644
--- a/src/expr.c
+++ b/src/expr.c
@@ -1568,24 +1568,22 @@ int sqlite3IsRowid(const char *z){
 }
 
 /*
-** Return true if we are able to the IN operator optimization on a
-** query of the form
-**
-**       x IN (SELECT ...)
-**
-** Where the SELECT... clause is as specified by the parameter to this
-** routine.
-**
-** The Select object passed in has already been preprocessed and no
-** errors have been found.
+** pX is the RHS of an IN operator.  If pX is a SELECT statement 
+** that can be simplified to a direct table access, then return
+** a pointer to the SELECT statement.  If pX is not a SELECT statement,
+** or if the SELECT statement needs to be manifested into a transient
+** table, then return NULL.
 */
 #ifndef SQLITE_OMIT_SUBQUERY
-static int isCandidateForInOpt(Select *p){
+static Select *isCandidateForInOpt(Expr *pX){
+  Select *p;
   SrcList *pSrc;
   ExprList *pEList;
+  Expr *pRes;
   Table *pTab;
-  Expr *pRes;                            /* Result expression */
-  if( p==0 ) return 0;                   /* right-hand side of IN is SELECT */
+  if( !ExprHasProperty(pX, EP_xIsSelect) ) return 0;  /* Not a subquery */
+  if( ExprHasProperty(pX, EP_VarSelect)  ) return 0;  /* Correlated subq */
+  p = pX->x.pSelect;
   if( p->pPrior ) return 0;              /* Not a compound SELECT */
   if( p->selFlags & (SF_Distinct|SF_Aggregate) ){
     testcase( (p->selFlags & (SF_Distinct|SF_Aggregate))==SF_Distinct );
@@ -1601,15 +1599,15 @@ static int isCandidateForInOpt(Select *p){
   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( NEVER(pTab==0) ) return 0;
+  assert( pTab!=0 );
   assert( pTab->pSelect==0 );            /* FROM clause is not a view */
   if( IsVirtual(pTab) ) return 0;        /* FROM clause not a virtual table */
   pEList = p->pEList;
   if( pEList->nExpr!=1 ) return 0;       /* One column in the result set */
   pRes = pEList->a[0].pExpr;
   if( pRes->op!=TK_COLUMN ) return 0;    /* Result is a column */
-  if( pRes->iTable!=pSrc->a[0].iCursor ) return 0;  /* Not a correlated subq */
-  return 1;
+  assert( pRes->iTable==pSrc->a[0].iCursor );  /* Not a correlated subquery */
+  return p;
 }
 #endif /* SQLITE_OMIT_SUBQUERY */
 
@@ -1741,15 +1739,13 @@ int sqlite3FindInIndex(Parse *pParse, Expr *pX, u32 inFlags, int *prRhsHasNull){
   ** satisfy the query.  This is preferable to generating a new 
   ** ephemeral table.
   */
-  p = (ExprHasProperty(pX, EP_xIsSelect) ? pX->x.pSelect : 0);
-  if( pParse->nErr==0 && isCandidateForInOpt(p) ){
+  if( pParse->nErr==0 && (p = isCandidateForInOpt(pX))!=0 ){
     sqlite3 *db = pParse->db;              /* Database connection */
     Table *pTab;                           /* Table <table>. */
     Expr *pExpr;                           /* Expression <column> */
     i16 iCol;                              /* Index of column <column> */
     i16 iDb;                               /* Database idx for pTab */
 
-    assert( p );                        /* Because of isCandidateForInOpt(p) */
     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) */