diff options
Diffstat (limited to 'src/select.c')
| -rw-r--r-- | src/select.c | 41 |
1 files changed, 41 insertions, 0 deletions
diff --git a/src/select.c b/src/select.c index 3128d482a..52586d8ca 100644 --- a/src/select.c +++ b/src/select.c @@ -3582,6 +3582,41 @@ static void substSelect( #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. ** This routine returns 1 if it makes changes and 0 if no flattening occurs. ** @@ -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 |