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Recompute the set of columns used for each table when the table is

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involved in query flattening.

FossilOrigin-Name: a9bb71ba708ba72255ba8d18c9856e38ddf53eae2d61c8435149354fb2b2459e
This commit is contained in:
drh
2020-03-21 00:05:53 +00:00
parent ec8e689a20
commit 2aee514b4c
5 changed files with 62 additions and 19 deletions
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41
src/select.c
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@@ -3580,6 +3580,41 @@ static void substSelect(
}
#endif /* !defined(SQLITE_OMIT_SUBQUERY) || !defined(SQLITE_OMIT_VIEW) */
#if !defined(SQLITE_OMIT_SUBQUERY) || !defined(SQLITE_OMIT_VIEW)
/*
** pSelect is a SELECT statement and pSrcItem is one item in the FROM
** clause of that SELECT.
**
** This routine scans the entire SELECT statement and recomputes the
** pSrcItem->colUsed mask.
*/
static int recomputeColumnsUsedExpr(Walker *pWalker, Expr *pExpr){
struct SrcList_item *pItem;
ynVar iCol;
if( pExpr->op!=TK_COLUMN ) return WRC_Continue;
pItem = pWalker->u.pSrcItem;
if( pItem->iCursor!=pExpr->iTable ) return WRC_Continue;
iCol = pExpr->iColumn;
if( iCol<0 ) return WRC_Continue;
if( iCol>=BMS ) iCol = BMS-1;
pItem->colUsed |= ((Bitmask)1)<<iCol;
return WRC_Continue;
}
static void recomputeColumnsUsed(
Select *pSelect, /* The complete SELECT statement */
struct SrcList_item *pSrcItem /* Which FROM clause item to recompute */
){
Walker w;
if( NEVER(pSrcItem->pTab==0) ) return;
memset(&w, 0, sizeof(w));
w.xExprCallback = recomputeColumnsUsedExpr;
w.xSelectCallback = sqlite3SelectWalkNoop;
w.u.pSrcItem = pSrcItem;
pSrcItem->colUsed = 0;
sqlite3WalkSelect(&w, pSelect);
}
#endif /* !defined(SQLITE_OMIT_SUBQUERY) || !defined(SQLITE_OMIT_VIEW) */
#if !defined(SQLITE_OMIT_SUBQUERY) || !defined(SQLITE_OMIT_VIEW)
/*
** This routine attempts to flatten subqueries as a performance optimization.
@@ -4118,6 +4153,12 @@ static int flattenSubquery(
pParent->pLimit = pSub->pLimit;
pSub->pLimit = 0;
}
/* Recompute the SrcList_item.colUsed masks for the flattened
** tables. */
for(i=0; i<nSubSrc; i++){
recomputeColumnsUsed(pParent, &pSrc->a[i+iFrom]);
}
}
/* Finially, delete what is left of the subquery and return