Fix ruleutils' get_variable() to print something useful for Vars referencing

resjunk outputs of subquery tlists, instead of throwing an error.  Per bug
#5548 from Daniel Grace.

We might at some point find we ought to back-patch this further than 9.0,
but I think that such Vars can only occur as resjunk members of upper-level
tlists, in which case the problem can't arise because prior versions didn't
print resjunk tlist items in EXPLAIN VERBOSE.

diff --git a/src/backend/utils/adt/ruleutils.c b/src/backend/utils/adt/ruleutils.c
index 54b6018d8e48d0fb6748b77661e008dda67fbddc..8b99c95070d8eb7c3ba787231df44a983a8d424d 100644 (file)
--- a/src/backend/utils/adt/ruleutils.c
+++ b/src/backend/utils/adt/ruleutils.c
@@ -9,7 +9,7 @@
  *
  *
  * IDENTIFICATION
- *       $PostgreSQL: pgsql/src/backend/utils/adt/ruleutils.c,v 1.326 2010/05/30 18:10:41 tgl Exp $
+ *       $PostgreSQL: pgsql/src/backend/utils/adt/ruleutils.c,v 1.327 2010/07/09 21:11:47 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -3637,6 +3637,49 @@ get_variable(Var *var, int levelsup, bool showstar, deparse_context *context)
                return NULL;                    /* keep compiler quiet */
        }
 
+       /*
+        * The planner will sometimes emit Vars referencing resjunk elements of a
+        * subquery's target list (this is currently only possible if it chooses
+        * to generate a "physical tlist" for a SubqueryScan or CteScan node).
+        * Although we prefer to print subquery-referencing Vars using the
+        * subquery's alias, that's not possible for resjunk items since they have
+        * no alias.  So in that case, drill down to the subplan and print the
+        * contents of the referenced tlist item.  This works because in a plan
+        * tree, such Vars can only occur in a SubqueryScan or CteScan node,
+        * and we'll have set dpns->inner_plan to reference the child plan node.
+        */
+       if ((rte->rtekind == RTE_SUBQUERY || rte->rtekind == RTE_CTE) &&
+               attnum > list_length(rte->eref->colnames) &&
+               dpns->inner_plan)
+       {
+               TargetEntry *tle;
+               Plan       *save_outer;
+               Plan       *save_inner;
+
+               tle = get_tle_by_resno(dpns->inner_plan->targetlist, var->varattno);
+               if (!tle)
+                       elog(ERROR, "bogus varattno for subquery var: %d", var->varattno);
+
+               Assert(netlevelsup == 0);
+               save_outer = dpns->outer_plan;
+               save_inner = dpns->inner_plan;
+               push_plan(dpns, dpns->inner_plan);
+
+               /*
+                * Force parentheses because our caller probably assumed a Var is a
+                * simple expression.
+                */
+               if (!IsA(tle->expr, Var))
+                       appendStringInfoChar(buf, '(');
+               get_rule_expr((Node *) tle->expr, context, true);
+               if (!IsA(tle->expr, Var))
+                       appendStringInfoChar(buf, ')');
+
+               dpns->outer_plan = save_outer;
+               dpns->inner_plan = save_inner;
+               return NULL;
+       }
+
        /* Identify names to use */
        schemaname = NULL;                      /* default assumptions */
        refname = rte->eref->aliasname;