@ -7,7 +7,7 @@
*
*
* IDENTIFICATION
* $ Header : / cvsroot / pgsql / src / backend / executor / execQual . c , v 1.65 2000 / 01 / 10 17 : 14 : 34 momjian Exp $
* $ Header : / cvsroot / pgsql / src / backend / executor / execQual . c , v 1.66 2000 / 01 / 19 23 : 54 : 54 tgl Exp $
*
* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
*/
@ -1283,12 +1283,33 @@ ExecEvalExpr(Node *expression,
/* ----------------------------------------------------------------
* ExecQual
*
* Evaluates a conjunctive boolean expression and returns t
* iff none of the subexpressions are false ( or null ) .
* Evaluates a conjunctive boolean expression ( qual list ) and
* returns true iff none of the subexpressions are false .
* ( We also return true if the list is empty . )
*
* If some of the subexpressions yield NULL but none yield FALSE ,
* then the result of the conjunction is NULL ( ie , unknown )
* according to three - valued boolean logic . In this case ,
* we return the value specified by the " resultForNull " parameter .
*
* Callers evaluating WHERE clauses should pass resultForNull = FALSE ,
* since SQL specifies that tuples with null WHERE results do not
* get selected . On the other hand , callers evaluating constraint
* conditions should pass resultForNull = TRUE , since SQL also specifies
* that NULL constraint conditions are not failures .
*
* NOTE : it would not be correct to use this routine to evaluate an
* AND subclause of a boolean expression ; for that purpose , a NULL
* result must be returned as NULL so that it can be properly treated
* in the next higher operator ( cf . ExecEvalAnd and ExecEvalOr ) .
* This routine is only used in contexts where a complete expression
* is being evaluated and we know that NULL can be treated the same
* as one boolean result or the other .
*
* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
*/
bool
ExecQual ( List * qual , ExprContext * econtext )
ExecQual ( List * qual , ExprContext * econtext , bool resultForNull )
{
List * qlist ;
@ -1302,18 +1323,18 @@ ExecQual(List *qual, ExprContext *econtext)
IncrProcessed ( ) ;
/*
* a " qual " is a list of clauses . To evaluate the qual , we evaluate
* each of the clauses in the list . ( For an empty list , we ' ll return
* TRUE . )
* Evaluate the qual conditions one at a time . If we find a FALSE
* result , we can stop evaluating and return FALSE - - - the AND result
* must be FALSE . Also , if we find a NULL result when resultForNull
* is FALSE , we can stop and return FALSE - - - the AND result must be
* FALSE or NULL in that case , and the caller doesn ' t care which .
*
* If any of the clauses return NULL , we treat this as FALSE . This
* is correct per the SQL spec : if any ANDed conditions are NULL , then
* the AND result is either FALSE or NULL , and in either case the
* WHERE condition fails . NOTE : it would NOT be correct to use this
* simplified logic in a sub - clause ; ExecEvalAnd must do the full
* three - state condition evaluation . We can get away with simpler
* logic here because we know how the result will be used .
* If we get to the end of the list , we can return TRUE . This will
* happen when the AND result is indeed TRUE , or when the AND result
* is NULL ( one or more NULL subresult , with all the rest TRUE ) and
* the caller has specified resultForNull = TRUE .
*/
foreach ( qlist , qual )
{
Node * clause = ( Node * ) lfirst ( qlist ) ;
@ -1321,7 +1342,11 @@ ExecQual(List *qual, ExprContext *econtext)
bool isNull ;
bool isDone ;
/* if there is a null clause, consider the qualification to fail */
/*
* If there is a null clause , consider the qualification to fail .
* XXX is this still correct for constraints ? It probably shouldn ' t
* happen at all . . .
*/
if ( clause = = NULL )
return false ;
/*
@ -1329,10 +1354,17 @@ ExecQual(List *qual, ExprContext *econtext)
* in the qualifications .
*/
expr_value = ExecEvalExpr ( clause , econtext , & isNull , & isDone ) ;
if ( isNull )
return false ; /* treat NULL as FALSE */
if ( DatumGetInt32 ( expr_value ) = = 0 )
return false ;
{
if ( resultForNull = = false )
return false ; /* treat NULL as FALSE */
}
else
{
if ( DatumGetInt32 ( expr_value ) = = 0 )
return false ; /* definitely FALSE */
}
}
return true ;
Tom Lane
26 years ago