Fix incorrect printing of queries with duplicated join names.

Given a query in which multiple JOIN nodes used the same alias
(which'd necessarily be in different sub-SELECTs), ruleutils.c
would assign the JOIN nodes distinct aliases for clarity ...
but then it forgot to print the modified aliases when dumping
the JOIN nodes themselves.  This results in a dump/reload hazard
for views, because the emitted query is flat-out incorrect:
Vars will be printed with table names that have no referent.

This has been wrong for a long time, so back-patch to all supported
branches.

Philip Dubé

Discussion: https://postgr.es/m/CY4PR2101MB080246F2955FF58A6ED1FEAC98140@CY4PR2101MB0802.namprd21.prod.outlook.com

1 files changed, 9 insertions, 1 deletions

diff --git a/src/backend/utils/adt/ruleutils.c b/src/backend/utils/adt/ruleutils.c
index c968213b8f9..f6f2b7c529d 100644
--- a/src/backend/utils/adt/ruleutils.c
+++ b/src/backend/utils/adt/ruleutils.c
@@ -9501,8 +9501,16 @@ get_from_clause_item(Node *jtnode, Query *query, deparse_context *context)
 		/* Yes, it's correct to put alias after the right paren ... */
 		if (j->alias != NULL)
 		{
+			/*
+			 * Note that it's correct to emit an alias clause if and only if
+			 * there was one originally.  Otherwise we'd be converting a named
+			 * join to unnamed or vice versa, which creates semantic
+			 * subtleties we don't want.  However, we might print a different
+			 * alias name than was there originally.
+			 */
 			appendStringInfo(buf, " %s",
-							 quote_identifier(j->alias->aliasname));
+							 quote_identifier(get_rtable_name(j->rtindex,
+															  context)));
 			get_column_alias_list(colinfo, context);
 		}
 	}