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Query planner optimization to detect empty tables in a join early and bail out

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without doing excess work.

FossilOrigin-Name: 58797e9bafa95709e0f706a15f42f93b409e2db5
This commit is contained in:
drh
2017-02-15 22:36:15 +00:00
parent 0d5b3b7665
commit 3a3b420abb
4 changed files with 67 additions and 10 deletions
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10
src/wherecode.c
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@ -1062,6 +1062,7 @@ Bitmask sqlite3WhereCodeOneLoopStart(
Vdbe *v; /* The prepared stmt under constructions */
struct SrcList_item *pTabItem; /* FROM clause term being coded */
int addrBrk; /* Jump here to break out of the loop */
int addrHalt; /* addrBrk for the outermost loop */
int addrCont; /* Jump here to continue with next cycle */
int iRowidReg = 0; /* Rowid is stored in this register, if not zero */
int iReleaseReg = 0; /* Temp register to free before returning */
@ -1103,6 +1104,11 @@ Bitmask sqlite3WhereCodeOneLoopStart(
VdbeComment((v, "init LEFT JOIN no-match flag"));
}
/* Compute a safe address to jump to if we discover that the table for
** this loop is empty and can never contribute content. */
for(j=iLevel; j>0 && pWInfo->a[j].iLeftJoin==0; j--){}
addrHalt = pWInfo->a[j].addrBrk;
/* Special case of a FROM clause subquery implemented as a co-routine */
if( pTabItem->fg.viaCoroutine ){
int regYield = pTabItem->regReturn;
@ -1287,7 +1293,7 @@ Bitmask sqlite3WhereCodeOneLoopStart(
sqlite3ExprCacheAffinityChange(pParse, r1, 1);
sqlite3ReleaseTempReg(pParse, rTemp);
}else{
sqlite3VdbeAddOp2(v, bRev ? OP_Last : OP_Rewind, iCur, addrBrk);
sqlite3VdbeAddOp2(v, bRev ? OP_Last : OP_Rewind, iCur, addrHalt);
VdbeCoverageIf(v, bRev==0);
VdbeCoverageIf(v, bRev!=0);
}
@ -1933,7 +1939,7 @@ Bitmask sqlite3WhereCodeOneLoopStart(
codeCursorHint(pTabItem, pWInfo, pLevel, 0);
pLevel->op = aStep[bRev];
pLevel->p1 = iCur;
pLevel->p2 = 1 + sqlite3VdbeAddOp2(v, aStart[bRev], iCur, addrBrk);
pLevel->p2 = 1 + sqlite3VdbeAddOp2(v, aStart[bRev], iCur, addrHalt);
VdbeCoverageIf(v, bRev==0);
VdbeCoverageIf(v, bRev!=0);
pLevel->p5 = SQLITE_STMTSTATUS_FULLSCAN_STEP;