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Attempt to optimize "x IS NULL" and "x IS NOT NULL" expressions when x is a column with a NOT NULL constraint.

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FossilOrigin-Name: 5ecd842555009ce27ee6390325ac5c2504143474b12b730933f0833b3dad788a
This commit is contained in:
dan
2021-02-26 20:14:32 +00:00
parent 4b17455ab2
commit 8ddf686267
6 changed files with 150 additions and 9 deletions
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38
src/resolve.c
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@@ -785,6 +785,44 @@ static int resolveExprStep(Walker *pWalker, Expr *pExpr){
break;
}
/* An "<expr> IS NOT NULL" or "<expr> IS NULL". After resolving the
** LHS, check if there is a NOT NULL constraint in the schema that
** means the value of the expression can be determined immediately.
** If that is the case, replace the current expression node with
** a TK_TRUEFALSE node.
**
** If the node is replaced with a TK_TRUEFALSE node, then also restore
** the NameContext ref-counts to the state they where in before the
** LHS expression was resolved. This prevents the current select
** from being erroneously marked as correlated in some cases.
*/
case TK_NOTNULL:
case TK_ISNULL: {
int anRef[8];
NameContext *p;
int i;
for(i=0, p=pNC; p && i<ArraySize(anRef); p=p->pNext, i++){
anRef[i] = p->nRef;
}
sqlite3WalkExpr(pWalker, pExpr->pLeft);
if( 0==sqlite3ExprCanBeNull(pExpr->pLeft) ){
if( pExpr->op==TK_NOTNULL ){
pExpr->u.zToken = "true";
ExprSetProperty(pExpr, EP_IsTrue);
}else{
pExpr->u.zToken = "false";
ExprSetProperty(pExpr, EP_IsFalse);
}
pExpr->op = TK_TRUEFALSE;
for(i=0, p=pNC; p && i<ArraySize(anRef); p=p->pNext, i++){
p->nRef = anRef[i];
}
sqlite3ExprDelete(pParse->db, pExpr->pLeft);
pExpr->pLeft = 0;
}
return WRC_Prune;
}
/* A column name: ID
** Or table name and column name: ID.ID
** Or a database, table and column: ID.ID.ID