When the [https://www.sqlite.org/queryplanner.html#partialsort|block sorting optimization]

is used in a scalar subquery, be sure to exit the loop as soon as the first
valid output row is received.  Fix for ticket [cb3aa0641d9a4].

FossilOrigin-Name: cdbb0947f9ce18d6d7e29ffab5ea6a2ee5365fbb

1 files changed, 12 insertions, 9 deletions

diff --git a/src/select.c b/src/select.c
index 0e7c4595d..fd094d05d 100644
--- a/src/select.c
+++ b/src/select.c
@@ -54,6 +54,7 @@ struct SortCtx {
   int regReturn;        /* Register holding block-output return address */
   int labelBkOut;       /* Start label for the block-output subroutine */
   int addrSortIndex;    /* Address of the OP_SorterOpen or OP_OpenEphemeral */
+  int labelDone;        /* Jump here when done, ex: LIMIT reached */
   u8 sortFlags;         /* Zero or more SORTFLAG_* bits */
 };
 #define SORTFLAG_UseSorter  0x01   /* Use SorterOpen instead of OpenEphemeral */
@@ -516,6 +517,7 @@ static void pushOntoSorter(
   int regRecord = ++pParse->nMem;                  /* Assembled sorter record */
   int nOBSat = pSort->nOBSat;                      /* ORDER BY terms to skip */
   int op;                            /* Opcode to add sorter record to sorter */
+  int iLimit;                        /* LIMIT counter */
 
   assert( bSeq==0 || bSeq==1 );
   assert( nData==1 || regData==regOrigData );
@@ -526,6 +528,9 @@ static void pushOntoSorter(
     regBase = pParse->nMem + 1;
     pParse->nMem += nBase;
   }
+  assert( pSelect->iOffset==0 || pSelect->iLimit!=0 );
+  iLimit = pSelect->iOffset ? pSelect->iOffset+1 : pSelect->iLimit;
+  pSort->labelDone = sqlite3VdbeMakeLabel(v);
   sqlite3ExprCodeExprList(pParse, pSort->pOrderBy, regBase, regOrigData,
                           SQLITE_ECEL_DUP|SQLITE_ECEL_REF);
   if( bSeq ){
@@ -534,7 +539,6 @@ static void pushOntoSorter(
   if( nPrefixReg==0 ){
     sqlite3ExprCodeMove(pParse, regData, regBase+nExpr+bSeq, nData);
   }
-
   sqlite3VdbeAddOp3(v, OP_MakeRecord, regBase+nOBSat, nBase-nOBSat, regRecord);
   if( nOBSat>0 ){
     int regPrevKey;   /* The first nOBSat columns of the previous row */
@@ -569,6 +573,10 @@ static void pushOntoSorter(
     pSort->regReturn = ++pParse->nMem;
     sqlite3VdbeAddOp2(v, OP_Gosub, pSort->regReturn, pSort->labelBkOut);
     sqlite3VdbeAddOp1(v, OP_ResetSorter, pSort->iECursor);
+    if( iLimit ){
+      sqlite3VdbeAddOp2(v, OP_IfNot, iLimit, pSort->labelDone);
+      VdbeCoverage(v);
+    }
     sqlite3VdbeJumpHere(v, addrFirst);
     sqlite3ExprCodeMove(pParse, regBase, regPrevKey, pSort->nOBSat);
     sqlite3VdbeJumpHere(v, addrJmp);
@@ -579,14 +587,8 @@ static void pushOntoSorter(
     op = OP_IdxInsert;
   }
   sqlite3VdbeAddOp2(v, op, pSort->iECursor, regRecord);
-  if( pSelect->iLimit ){
+  if( iLimit ){
     int addr;
-    int iLimit;
-    if( pSelect->iOffset ){
-      iLimit = pSelect->iOffset+1;
-    }else{
-      iLimit = pSelect->iLimit;
-    }
     addr = sqlite3VdbeAddOp3(v, OP_IfNotZero, iLimit, 0, 1); VdbeCoverage(v);
     sqlite3VdbeAddOp1(v, OP_Last, pSort->iECursor);
     sqlite3VdbeAddOp1(v, OP_Delete, pSort->iECursor);
@@ -1190,7 +1192,7 @@ static void generateSortTail(
   SelectDest *pDest /* Write the sorted results here */
 ){
   Vdbe *v = pParse->pVdbe;                     /* The prepared statement */
-  int addrBreak = sqlite3VdbeMakeLabel(v);     /* Jump here to exit loop */
+  int addrBreak = pSort->labelDone;            /* Jump here to exit loop */
   int addrContinue = sqlite3VdbeMakeLabel(v);  /* Jump here for next cycle */
   int addr;
   int addrOnce = 0;
@@ -1209,6 +1211,7 @@ static void generateSortTail(
   struct ExprList_item *aOutEx = p->pEList->a;
 #endif
 
+  assert( addrBreak<0 );
   if( pSort->labelBkOut ){
     sqlite3VdbeAddOp2(v, OP_Gosub, pSort->regReturn, pSort->labelBkOut);
     sqlite3VdbeGoto(v, addrBreak);