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Improved comments on the OR-optimization logic in the query planner.

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FossilOrigin-Name: 77fef5a3987fc16f84a8e755283ca6ec1363013c
This commit is contained in:
drh
2014-05-27 16:41:39 +00:00
parent f53b4ad0f9
commit 3fb6730699
3 changed files with 24 additions and 10 deletions
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20
src/where.c
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@@ -3401,12 +3401,16 @@ static Bitmask codeOneLoopStart(
}
}
/* Run a separate WHERE clause for each term of the OR clause. After
** eliminating duplicates from other WHERE clauses, the action for each
** sub-WHERE clause is to to invoke the main loop body as a subroutine.
*/
for(ii=0; ii<pOrWc->nTerm; ii++){
WhereTerm *pOrTerm = &pOrWc->a[ii];
if( pOrTerm->leftCursor==iCur || (pOrTerm->eOperator & WO_AND)!=0 ){
WhereInfo *pSubWInfo; /* Info for single OR-term scan */
Expr *pOrExpr = pOrTerm->pExpr;
int j1 = 0; /* Address of jump operation */
WhereInfo *pSubWInfo; /* Info for single OR-term scan */
Expr *pOrExpr = pOrTerm->pExpr; /* Current OR clause term */
int j1 = 0; /* Address of jump operation */
if( pAndExpr && !ExprHasProperty(pOrExpr, EP_FromJoin) ){
pAndExpr->pLeft = pOrExpr;
pOrExpr = pAndExpr;
@@ -3421,6 +3425,11 @@ static Bitmask codeOneLoopStart(
explainOneScan(
pParse, pOrTab, &pSubWInfo->a[0], iLevel, pLevel->iFrom, 0
);
/* This is the sub-WHERE clause body. First skip over
** duplicate rows from prior sub-WHERE clauses, and record the
** rowid (or PRIMARY KEY) for the current row so that the same
** row will be skipped in subsequent sub-WHERE clauses.
*/
if( (pWInfo->wctrlFlags & WHERE_DUPLICATES_OK)==0 ){
int r;
int iSet = ((ii==pOrWc->nTerm-1)?-1:ii);
@@ -3465,7 +3474,12 @@ static Bitmask codeOneLoopStart(
sqlite3ReleaseTempRange(pParse, r, nPk);
}
}
/* Invoke the main loop body as a subroutine */
sqlite3VdbeAddOp2(v, OP_Gosub, regReturn, iLoopBody);
/* Jump here (skipping the main loop body subroutine) if the
** current sub-WHERE row is a duplicate from prior sub-WHEREs. */
if( j1 ) sqlite3VdbeJumpHere(v, j1);
/* The pSubWInfo->untestedTerms flag means that this OR term