diff options
Diffstat (limited to 'src/backend/parser/parse_relation.c')
| -rw-r--r-- | src/backend/parser/parse_relation.c | 15 |
1 files changed, 13 insertions, 2 deletions
diff --git a/src/backend/parser/parse_relation.c b/src/backend/parser/parse_relation.c index 42de89f5101..d473749e303 100644 --- a/src/backend/parser/parse_relation.c +++ b/src/backend/parser/parse_relation.c @@ -131,6 +131,18 @@ refnameRangeTblEntry(ParseState *pstate, * Search the query's table namespace for an RTE matching the * given unqualified refname. Return the RTE if a unique match, or NULL * if no match. Raise error if multiple matches. + * + * Note: it might seem that we shouldn't have to worry about the possibility + * of multiple matches; after all, the SQL standard disallows duplicate table + * aliases within a given SELECT level. Historically, however, Postgres has + * been laxer than that. For example, we allow + * SELECT ... FROM tab1 x CROSS JOIN (tab2 x CROSS JOIN tab3 y) z + * on the grounds that the aliased join (z) hides the aliases within it, + * therefore there is no conflict between the two RTEs named "x". However, + * if tab3 is a LATERAL subquery, then from within the subquery both "x"es + * are visible. Rather than rejecting queries that used to work, we allow + * this situation, and complain only if there's actually an ambiguous + * reference to "x". */ static RangeTblEntry * scanNameSpaceForRefname(ParseState *pstate, const char *refname, int location) @@ -175,8 +187,7 @@ scanNameSpaceForRefname(ParseState *pstate, const char *refname, int location) /* * Search the query's table namespace for a relation RTE matching the * given relation OID. Return the RTE if a unique match, or NULL - * if no match. Raise error if multiple matches (which shouldn't - * happen if the namespace was checked correctly when it was created). + * if no match. Raise error if multiple matches. * * See the comments for refnameRangeTblEntry to understand why this * acts the way it does. |