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Use transitivity to move constraints into the outer loops of a join whenever

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possible, thereby reducing the amount of work that needs to occur in
inner loops.

FossilOrigin-Name: 5f4907e1c6230e3dd904bd99e1c48c576c669f63
This commit is contained in:
drh
2013-04-22 02:39:10 +00:00
parent cca17c303b
commit 0c41d22920
3 changed files with 39 additions and 11 deletions
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36
src/where.c
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@@ -4161,6 +4161,7 @@ static Bitmask codeOneLoopStart(
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 */
Bitmask newNotReady; /* Return value */
pParse = pWInfo->pParse;
v = pParse->pVdbe;
@@ -4171,6 +4172,7 @@ static Bitmask codeOneLoopStart(
bRev = (pLevel->plan.wsFlags & WHERE_REVERSE)!=0;
omitTable = (pLevel->plan.wsFlags & WHERE_IDX_ONLY)!=0
&& (wctrlFlags & WHERE_FORCE_TABLE)==0;
VdbeNoopComment((v, "Begin Join Loop %d", iLevel));
/* Create labels for the "break" and "continue" instructions
** for the current loop. Jump to addrBrk to break out of a loop.
@@ -4821,7 +4823,7 @@ static Bitmask codeOneLoopStart(
pLevel->p2 = 1 + sqlite3VdbeAddOp2(v, aStart[bRev], iCur, addrBrk);
pLevel->p5 = SQLITE_STMTSTATUS_FULLSCAN_STEP;
}
notReady &= ~getMask(pWC->pMaskSet, iCur);
newNotReady = notReady & ~getMask(pWC->pMaskSet, iCur);
/* Insert code to test every subexpression that can be completely
** computed using the current set of tables.
@@ -4835,7 +4837,7 @@ static Bitmask codeOneLoopStart(
testcase( pTerm->wtFlags & TERM_VIRTUAL ); /* IMP: R-30575-11662 */
testcase( pTerm->wtFlags & TERM_CODED );
if( pTerm->wtFlags & (TERM_VIRTUAL|TERM_CODED) ) continue;
if( (pTerm->prereqAll & notReady)!=0 ){
if( (pTerm->prereqAll & newNotReady)!=0 ){
testcase( pWInfo->untestedTerms==0
&& (pWInfo->wctrlFlags & WHERE_ONETABLE_ONLY)!=0 );
pWInfo->untestedTerms = 1;
@@ -4850,6 +4852,32 @@ static Bitmask codeOneLoopStart(
pTerm->wtFlags |= TERM_CODED;
}
/* Insert code to test for implied constraints based on transitivity
** of the "==" operator.
**
** Example: If the WHERE clause contains "t1.a=t2.b" and "t2.b=123"
** and we are coding the t1 loop and the t2 loop has not yet coded,
** then we cannot use the "t1.a=t2.b" constraint, but we can code
** the implied "t1.a=123" constraint.
*/
for(pTerm=pWC->a, j=pWC->nTerm; j>0; j--, pTerm++){
Expr *pE;
WhereTerm *pAlt;
Expr sEq;
if( pTerm->wtFlags & (TERM_VIRTUAL|TERM_CODED) ) continue;
if( pTerm->eOperator!=(WO_EQUIV|WO_EQ) ) continue;
if( pTerm->leftCursor!=iCur ) continue;
pE = pTerm->pExpr;
assert( !ExprHasProperty(pE, EP_FromJoin) );
assert( (pTerm->prereqRight & newNotReady)!=0 );
pAlt = findTerm(pWC, iCur, pTerm->u.leftColumn, notReady, WO_EQ|WO_IN, 0);
if( pAlt==0 ) continue;
VdbeNoopComment((v, "begin transitive constraint"));
sEq = *pAlt->pExpr;
sEq.pLeft = pE->pLeft;
sqlite3ExprIfFalse(pParse, &sEq, addrCont, SQLITE_JUMPIFNULL);
}
/* For a LEFT OUTER JOIN, generate code that will record the fact that
** at least one row of the right table has matched the left table.
*/
@@ -4862,7 +4890,7 @@ static Bitmask codeOneLoopStart(
testcase( pTerm->wtFlags & TERM_VIRTUAL ); /* IMP: R-30575-11662 */
testcase( pTerm->wtFlags & TERM_CODED );
if( pTerm->wtFlags & (TERM_VIRTUAL|TERM_CODED) ) continue;
if( (pTerm->prereqAll & notReady)!=0 ){
if( (pTerm->prereqAll & newNotReady)!=0 ){
assert( pWInfo->untestedTerms );
continue;
}
@@ -4873,7 +4901,7 @@ static Bitmask codeOneLoopStart(
}
sqlite3ReleaseTempReg(pParse, iReleaseReg);
return notReady;
return newNotReady;
}
#if defined(SQLITE_TEST)