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Do more aggressive optimization of the AND operator where one side or the

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other is always false.

FossilOrigin-Name: f9a7e179cbbeeab5e57bbf392bef89750215546b
This commit is contained in:
drh
2012-03-31 02:34:35 +00:00
parent 00fa55d7da
commit 5fb52caadf
4 changed files with 56 additions and 12 deletions
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36
src/expr.c
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@@ -484,23 +484,55 @@ Expr *sqlite3PExpr(
Expr *pRight, /* Right operand */
const Token *pToken /* Argument token */
){
Expr *p = sqlite3ExprAlloc(pParse->db, op, pToken, 1);
sqlite3ExprAttachSubtrees(pParse->db, p, pLeft, pRight);
Expr *p;
if( op==TK_AND && pLeft && pRight ){
/* Take advantage of short-circuit false optimization for AND */
p = sqlite3ExprAnd(pParse->db, pLeft, pRight);
}else{
p = sqlite3ExprAlloc(pParse->db, op, pToken, 1);
sqlite3ExprAttachSubtrees(pParse->db, p, pLeft, pRight);
}
if( p ) {
sqlite3ExprCheckHeight(pParse, p->nHeight);
}
return p;
}
/*
** Return 1 if an expression must be FALSE in all cases and 0 if the
** expression might be true. This is an optimization. If is OK to
** return 0 here even if the expression really is always false (a
** false negative). But it is a bug to return 1 if the expression
** might be true in some rare circumstances (a false positive.)
**
** Note that if the expression is part of conditional for a
** LEFT JOIN, then we cannot determine at compile-time whether or not
** is it true or false, so always return 0.
*/
static int exprAlwaysFalse(Expr *p){
int v = 0;
if( ExprHasProperty(p, EP_FromJoin) ) return 0;
if( !sqlite3ExprIsInteger(p, &v) ) return 0;
return v==0;
}
/*
** Join two expressions using an AND operator. If either expression is
** NULL, then just return the other expression.
**
** If one side or the other of the AND is known to be false, then instead
** of returning an AND expression, just return a constant expression with
** a value of false.
*/
Expr *sqlite3ExprAnd(sqlite3 *db, Expr *pLeft, Expr *pRight){
if( pLeft==0 ){
return pRight;
}else if( pRight==0 ){
return pLeft;
}else if( exprAlwaysFalse(pLeft) || exprAlwaysFalse(pRight) ){
sqlite3ExprDelete(db, pLeft);
sqlite3ExprDelete(db, pRight);
return sqlite3ExprAlloc(db, TK_INTEGER, &sqlite3IntTokens[0], 0);
}else{
Expr *pNew = sqlite3ExprAlloc(db, TK_AND, 0, 0);
sqlite3ExprAttachSubtrees(db, pNew, pLeft, pRight);