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;
 }