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If terms of the WHERE clause require that the right table in a LEFT JOIN

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not be a null row, then simplify the LEFT JOIN into an ordinary JOIN.

FossilOrigin-Name: 5b7abecc7ab8ccbbb8cb5e0f672e67625c2555ad03442efbf34cb395f5bb71a8
This commit is contained in:
drh
2018-03-20 21:16:15 +00:00
parent f6e6f02308
commit 2589787c5a
7 changed files with 109 additions and 14 deletions
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52
src/expr.c
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@@ -5001,6 +5001,58 @@ int sqlite3ExprImpliesExpr(Parse *pParse, Expr *pE1, Expr *pE2, int iTab){
return 0;
}
/*
** This is the Expr node callback for sqlite3ExprImpliesNotNullRow().
** If the expression node requires that the table at pWalker->iCur
** have a non-NULL column, then set pWalker->eCode to 1 and abort.
*/
static int impliesNotNullRow(Walker *pWalker, Expr *pExpr){
if( ExprHasProperty(pExpr, EP_FromJoin) ) return WRC_Prune;
switch( pExpr->op ){
case TK_ISNULL:
case TK_IS:
case TK_OR:
case TK_FUNCTION:
case TK_AGG_FUNCTION:
return WRC_Prune;
case TK_COLUMN:
case TK_AGG_COLUMN:
if( pWalker->u.iCur==pExpr->iTable ){
pWalker->eCode = 1;
return WRC_Abort;
}
return WRC_Prune;
default:
return WRC_Continue;
}
}
/*
** Return true (non-zero) if expression p can only be true if at least
** one column of table iTab is non-null. In other words, return true
** if expression p will always be NULL or false if every column of iTab
** is NULL.
**
** Terms of p that are marked with EP_FromJoin (and hence that come from
** the ON or USING clauses of LEFT JOINS) are excluded from the analysis.
**
** This routine is used to check if a LEFT JOIN can be converted into
** an ordinary JOIN. The p argument is the WHERE clause. If the WHERE
** clause requires that some column of the right table of the LEFT JOIN
** be non-NULL, then the LEFT JOIN can be safely converted into an
** ordinary join.
*/
int sqlite3ExprImpliesNonNullRow(Expr *p, int iTab){
Walker w;
w.xExprCallback = impliesNotNullRow;
w.xSelectCallback = 0;
w.xSelectCallback2 = 0;
w.eCode = 0;
w.u.iCur = iTab;
sqlite3WalkExpr(&w, p);
return w.eCode;
}
/*
** An instance of the following structure is used by the tree walker
** to determine if an expression can be evaluated by reference to the