diff options
Diffstat (limited to 'src/backend/executor/execQual.c')
| -rw-r--r-- | src/backend/executor/execQual.c | 68 |
1 files changed, 50 insertions, 18 deletions
diff --git a/src/backend/executor/execQual.c b/src/backend/executor/execQual.c index bd546597733..9e9cbde83bf 100644 --- a/src/backend/executor/execQual.c +++ b/src/backend/executor/execQual.c @@ -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; |