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The NOT NULL strength reduction optimization from [de9c86c9e4cdb34f] should

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be applied to the WHERE clause only.  Otherwise, the operand of the IS NULL
or IS NOT NULL operator might be a reference to a bare column of an
aggregate table, and we can't tell if it is NULL or not based only on its
NOT NULL attribute.  [forum:/forumpost/440f2a2f17|Forum post 440f2a2f17].

FossilOrigin-Name: 51704feae224eff601db5607f8651da11b3c2ed8a58ffe5b6ee8260cab50695b
This commit is contained in:
drh
2024-03-08 21:37:18 +00:00
parent 96f5ae6bd7
commit 61b77a6fe1
5 changed files with 67 additions and 25 deletions
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56
src/resolve.c
View File

@@ -971,6 +971,19 @@ static int resolveExprStep(Walker *pWalker, Expr *pExpr){
** resolved. This prevents "column" from being counted as having been
** referenced, which might prevent a SELECT from being erroneously
** marked as correlated.
**
** 2024-03-28: Beware of aggregates. A bare column of aggregated table
** can still evaluate to NULL even though it is marked as NOT NULL.
** Example:
**
** CREATE TABLE t1(a INT NOT NULL);
** SELECT a, a IS NULL, a IS NOT NULL, count(*) FROM t1;
**
** The "a IS NULL" and "a IS NOT NULL" expressions cannot be optimized
** here because at the time this case is hit, we do not yet know whether
** or not t1 is being aggregated. We have to assume the worst and omit
** the optimization. The only time it is safe to apply this optimization
** is within the WHERE clause.
*/
case TK_NOTNULL:
case TK_ISNULL: {
@@ -981,19 +994,36 @@ static int resolveExprStep(Walker *pWalker, Expr *pExpr){
anRef[i] = p->nRef;
}
sqlite3WalkExpr(pWalker, pExpr->pLeft);
if( 0==sqlite3ExprCanBeNull(pExpr->pLeft) && !IN_RENAME_OBJECT ){
testcase( ExprHasProperty(pExpr, EP_OuterON) );
assert( !ExprHasProperty(pExpr, EP_IntValue) );
pExpr->u.iValue = (pExpr->op==TK_NOTNULL);
pExpr->flags |= EP_IntValue;
pExpr->op = TK_INTEGER;
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;
if( IN_RENAME_OBJECT ) return WRC_Prune;
if( sqlite3ExprCanBeNull(pExpr->pLeft) ){
/* The expression can be NULL. So the optimization does not apply */
return WRC_Prune;
}
for(i=0, p=pNC; p; p=p->pNext, i++){
if( (p->ncFlags & NC_Where)==0 ){
return WRC_Prune; /* Not in a WHERE clause. Unsafe to optimize. */
}
}
testcase( ExprHasProperty(pExpr, EP_OuterON) );
assert( !ExprHasProperty(pExpr, EP_IntValue) );
#if TREETRACE_ENABLED
if( sqlite3TreeTrace & 0x80000 ){
sqlite3DebugPrintf(
"NOT NULL strength reduction converts the following to %d:\n",
pExpr->op==TK_NOTNULL
);
sqlite3ShowExpr(pExpr);
}
#endif /* TREETRACE_ENABLED */
pExpr->u.iValue = (pExpr->op==TK_NOTNULL);
pExpr->flags |= EP_IntValue;
pExpr->op = TK_INTEGER;
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;
}
@@ -1891,7 +1921,9 @@ static int resolveSelectStep(Walker *pWalker, Select *p){
}
if( sqlite3ResolveExprNames(&sNC, p->pHaving) ) return WRC_Abort;
}
sNC.ncFlags |= NC_Where;
if( sqlite3ResolveExprNames(&sNC, p->pWhere) ) return WRC_Abort;
sNC.ncFlags &= ~NC_Where;
/* Resolve names in table-valued-function arguments */
for(i=0; i<p->pSrc->nSrc; i++){

2
src/sqliteInt.h
View File

@@ -1125,6 +1125,7 @@ extern u32 sqlite3TreeTrace;
** 0x00010000 Beginning of DELETE/INSERT/UPDATE processing
** 0x00020000 Transform DISTINCT into GROUP BY
** 0x00040000 SELECT tree dump after all code has been generated
** 0x00080000 NOT NULL strength reduction
*/
/*
@@ -3453,6 +3454,7 @@ struct NameContext {
#define NC_InAggFunc 0x020000 /* True if analyzing arguments to an agg func */
#define NC_FromDDL 0x040000 /* SQL text comes from sqlite_schema */
#define NC_NoSelect 0x080000 /* Do not descend into sub-selects */
#define NC_Where 0x100000 /* Processing WHERE clause of a SELECT */
#define NC_OrderAgg 0x8000000 /* Has an aggregate other than count/min/max */
/*