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When testing non-indexed WHERE constraints, test those that involve

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correlated sub-queries last of all. This increases the chances of not having
to run the sub-query at all.

FossilOrigin-Name: 1f9c1f359e4693954ba7e2bc7b172ef34eb046e4ca2796df8336975b9d6aa92b
This commit is contained in:
dan
2017-07-10 14:33:00 +00:00
parent 9f6e14c1ef
commit ebc63013b7
4 changed files with 36 additions and 20 deletions
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33
src/wherecode.c
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@@ -1130,7 +1130,7 @@ Bitmask sqlite3WhereCodeOneLoopStart(
int iRowidReg = 0; /* Rowid is stored in this register, if not zero */
int iReleaseReg = 0; /* Temp register to free before returning */
Index *pIdx = 0; /* Index used by loop (if any) */
int loopAgain; /* True if constraint generator loop should repeat */
int iLoop; /* Iteration of constraint generator loop */
pParse = pWInfo->pParse;
v = pParse->pVdbe;
@@ -2025,13 +2025,20 @@ Bitmask sqlite3WhereCodeOneLoopStart(
/* Insert code to test every subexpression that can be completely
** computed using the current set of tables.
**
** This loop may run either once (pIdx==0) or twice (pIdx!=0). If
** it is run twice, then the first iteration codes those sub-expressions
** that can be computed using columns from pIdx only (without seeking
** the main table cursor).
** This loop may run between one and three times, depending on the
** constraints to be generated. The value of stack variable iLoop
** determines the constraints coded by each iteration, as follows:
**
** iLoop==1: Code only expressions that are entirely covered by pIdx.
** iLoop==2: Code remaining expressions that do not contain correlated
** sub-queries.
** iLoop==3: Code all remaining expressions.
**
** An effort is made to skip unnecessary iterations of the loop.
*/
iLoop = (pIdx ? 1 : 2);
do{
loopAgain = 0;
int iNext = 0; /* Next value for iLoop */
for(pTerm=pWC->a, j=pWC->nTerm; j>0; j--, pTerm++){
Expr *pE;
int skipLikeAddr = 0;
@@ -2049,10 +2056,16 @@ Bitmask sqlite3WhereCodeOneLoopStart(
if( pLevel->iLeftJoin && !ExprHasProperty(pE, EP_FromJoin) ){
continue;
}
if( pIdx && !sqlite3ExprCoveredByIndex(pE, pLevel->iTabCur, pIdx) ){
loopAgain = 1;
if( iNext==1 && !sqlite3ExprCoveredByIndex(pE, pLevel->iTabCur, pIdx) ){
iNext = 2;
continue;
}
if( iLoop<3 && (pE->flags & EP_VarSelect) ){
if( iNext==0 ) iNext = 3;
continue;
}
if( pTerm->wtFlags & TERM_LIKECOND ){
/* If the TERM_LIKECOND flag is set, that means that the range search
** is sufficient to guarantee that the LIKE operator is true, so we
@@ -2072,8 +2085,8 @@ Bitmask sqlite3WhereCodeOneLoopStart(
if( skipLikeAddr ) sqlite3VdbeJumpHere(v, skipLikeAddr);
pTerm->wtFlags |= TERM_CODED;
}
pIdx = 0;
}while( loopAgain );
iLoop = iNext;
}while( iLoop>0 );
/* Insert code to test for implied constraints based on transitivity
** of the "==" operator.