Fix oversight in recent changes to enable the 'physical tlist'

optimization for subquery and function scan nodes: we can't just do it
unconditionally, we still have to check whether there is any need for
a whole-row Var.  I had been thinking that these node types couldn't
have any system columns, which is true, but that loop is also checking
for attno zero, ie, whole-row Var.  Fix comment to not be so misleading.
Per test case from Richard Huxton.

diff --git a/src/backend/optimizer/plan/createplan.c b/src/backend/optimizer/plan/createplan.c
index f0dd6548711d6c8f756dbfc3eb0da94ae27b00e7..fc093fdf1800d92b41b3082d1033afdea6655a43 100644 (file)
--- a/src/backend/optimizer/plan/createplan.c
+++ b/src/backend/optimizer/plan/createplan.c
@@ -10,7 +10,7 @@
  *
  *
  * IDENTIFICATION
- *       $PostgreSQL: pgsql/src/backend/optimizer/plan/createplan.c,v 1.201 2005/10/15 02:49:20 momjian Exp $
+ *       $PostgreSQL: pgsql/src/backend/optimizer/plan/createplan.c,v 1.202 2005/10/19 17:31:20 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -308,17 +308,13 @@ use_physical_tlist(RelOptInfo *rel)
        int                     i;
 
        /*
-        * OK for subquery and function scans; otherwise, can't do it for anything
-        * except real relations.
+        * We can do this for real relation scans, subquery scans, and function
+        * scans (but not for, eg, joins).
         */
-       if (rel->rtekind != RTE_RELATION)
-       {
-               if (rel->rtekind == RTE_SUBQUERY)
-                       return true;
-               if (rel->rtekind == RTE_FUNCTION)
-                       return true;
+       if (rel->rtekind != RTE_RELATION &&
+               rel->rtekind != RTE_SUBQUERY &&
+               rel->rtekind != RTE_FUNCTION)
                return false;
-       }
 
        /*
         * Can't do it with inheritance cases either (mainly because Append
@@ -328,15 +324,16 @@ use_physical_tlist(RelOptInfo *rel)
                return false;
 
        /*
-        * Can't do it if any system columns are requested, either.  (This could
-        * possibly be fixed but would take some fragile assumptions in setrefs.c,
-        * I think.)
+        * Can't do it if any system columns or whole-row Vars are requested,
+        * either.  (This could possibly be fixed but would take some fragile
+        * assumptions in setrefs.c, I think.)
         */
        for (i = rel->min_attr; i <= 0; i++)
        {
                if (!bms_is_empty(rel->attr_needed[i - rel->min_attr]))
                        return false;
        }
+
        return true;
 }