2 files changed, 24 insertions, 16 deletions

diff --git a/src/backend/access/nbtree/nbtsearch.c b/src/backend/access/nbtree/nbtsearch.c
index 8f559629cd5..472ce06f190 100644
--- a/src/backend/access/nbtree/nbtsearch.c
+++ b/src/backend/access/nbtree/nbtsearch.c
@@ -1162,23 +1162,23 @@ _bt_first(IndexScanDesc scan, ScanDirection dir)
 		if (cur->sk_flags & SK_ROW_HEADER)
 		{
 			/*
-			 * Row comparison header: look to the first row member instead.
-			 *
-			 * The member scankeys are already in insertion format (ie, they
-			 * have sk_func = 3-way-comparison function), but we have to watch
-			 * out for nulls, which _bt_preprocess_keys didn't check. A null
-			 * in the first row member makes the condition unmatchable, just
-			 * like qual_ok = false.
+			 * Row comparison header: look to the first row member instead
 			 */
 			ScanKey		subkey = (ScanKey) DatumGetPointer(cur->sk_argument);
 
+			/*
+			 * Cannot be a NULL in the first row member: _bt_preprocess_keys
+			 * would've marked the qual as unsatisfiable, preventing us from
+			 * ever getting this far
+			 */
 			Assert(subkey->sk_flags & SK_ROW_MEMBER);
-			if (subkey->sk_flags & SK_ISNULL)
-			{
-				Assert(!so->needPrimScan);
-				_bt_parallel_done(scan);
-				return false;
-			}
+			Assert(subkey->sk_attno == cur->sk_attno);
+			Assert(!(subkey->sk_flags & SK_ISNULL));
+
+			/*
+			 * The member scankeys are already in insertion format (ie, they
+			 * have sk_func = 3-way-comparison function)
+			 */
 			memcpy(inskey.scankeys + i, subkey, sizeof(ScanKeyData));
 
 			/*
diff --git a/src/backend/access/nbtree/nbtutils.c b/src/backend/access/nbtree/nbtutils.c
index 268b7b02acd..00e17a1f0f9 100644
--- a/src/backend/access/nbtree/nbtutils.c
+++ b/src/backend/access/nbtree/nbtutils.c
@@ -3371,6 +3371,13 @@ _bt_fix_scankey_strategy(ScanKey skey, int16 *indoption)
 	{
 		ScanKey		subkey = (ScanKey) DatumGetPointer(skey->sk_argument);
 
+		if (subkey->sk_flags & SK_ISNULL)
+		{
+			/* First row member is NULL, so RowCompare is unsatisfiable */
+			Assert(subkey->sk_flags & SK_ROW_MEMBER);
+			return false;
+		}
+
 		for (;;)
 		{
 			Assert(subkey->sk_flags & SK_ROW_MEMBER);
@@ -3982,13 +3989,14 @@ _bt_check_rowcompare(ScanKey skey, IndexTuple tuple, int tupnatts,
 		if (subkey->sk_flags & SK_ISNULL)
 		{
 			/*
-			 * Unlike the simple-scankey case, this isn't a disallowed case.
+			 * Unlike the simple-scankey case, this isn't a disallowed case
+			 * (except when it's the first row element that has the NULL arg).
 			 * But it can never match.  If all the earlier row comparison
 			 * columns are required for the scan direction, we can stop the
 			 * scan, because there can't be another tuple that will succeed.
 			 */
-			if (subkey != (ScanKey) DatumGetPointer(skey->sk_argument))
-				subkey--;
+			Assert(subkey != (ScanKey) DatumGetPointer(skey->sk_argument));
+			subkey--;
 			if ((subkey->sk_flags & SK_BT_REQFWD) &&
 				ScanDirectionIsForward(dir))
 				*continuescan = false;