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Enable ORDER BY clauses that span joins to be optimized out.

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FossilOrigin-Name: c29538f9b1ee4d4869999570604c9618ca0d08ac
This commit is contained in:
drh
2012-09-27 14:11:36 +00:00
parent ff2d52117b
commit 32634d270c
3 changed files with 59 additions and 9 deletions
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54
src/where.c
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@@ -2863,17 +2863,67 @@ static int whereInScanEst(
}
#endif /* defined(SQLITE_ENABLE_STAT3) */
/*
** Check to see if column iCol of the table with cursor iTab will appear
** in sorted order according to the current query plan. Return true if
** it will and false if not.
**
** If *pbRev is initially 2 (meaning "unknown") then set *pbRev to the
** sort order of iTab.iCol. If *pbRev is 0 or 1 but does not match
** the sort order of iTab.iCol, then consider the column to be unordered.
*/
static int isOrderedColumn(WhereBestIdx *p, int iTab, int iCol, int *pbRev){
int i, j;
WhereLevel *pLevel = &p->aLevel[p->i-1];
Index *pIdx;
u8 sortOrder;
for(i=p->i-1; i>=0; i--, pLevel--){
if( pLevel->iTabCur!=iTab ) continue;
if( (pLevel->plan.wsFlags & (WHERE_ROWID_EQ|WHERE_ROWID_RANGE))!=0 ){
if( iCol!=(-1) ) return 0;
sortOrder = 0;
}else if( (pLevel->plan.wsFlags & WHERE_INDEXED)!=0 ){
pIdx = pLevel->plan.u.pIdx;
for(j=0; j<pIdx->nColumn; j++){
if( iCol==pIdx->aiColumn[j] ) break;
}
if( j>=pIdx->nColumn ) return 0;
sortOrder = pIdx->aSortOrder[j];
}else{
if( iCol!=(-1) ) return 0;
sortOrder = 0;
}
if( (pLevel->plan.wsFlags & WHERE_REVERSE)!=0 ) sortOrder = 1 - sortOrder;
if( *pbRev==2 ){
*pbRev = sortOrder;
return 1;
}
return (*pbRev==sortOrder);
}
return 0;
}
/*
** pTerm is an == constraint. Check to see if the other side of
** the == is a constant or a value that is guaranteed to be ordered
** by outer loops. Return 1 if pTerm is ordered, and 0 if not.
*/
static int isOrderedTerm(WhereBestIdx *p, WhereTerm *pTerm, int *pbRev){
Expr *pExpr = pTerm->pExpr;
assert( pExpr->op==TK_EQ );
assert( pExpr->pLeft!=0 && pExpr->pLeft->op==TK_COLUMN );
assert( pExpr->pRight!=0 );
if( p->i==0 ){
return 1; /* All == are ordered in the outer loop */
}
if( pTerm->prereqRight==0 ){
return 1; /* RHS of the == is a constant */
}
if( pExpr->pRight->op==TK_COLUMN
&& isOrderedColumn(p, pExpr->pRight->iTable, pExpr->pRight->iColumn, pbRev)
){
return 1;
}
/* If we cannot prove that the constraint is ordered, assume it is not */
return 0;