Re: index scan through a subquery

Bill Howe <howew@stccmop.org> writes:
> I need the lovely index scan, but my table is hidden behind a view, and
> all I get is the ugly sequential scan.  Any ideas on how to convince the
> optimizer to unfold the subquery properly?

You should provide some context in this sort of gripe, like which PG
version you're using.  But I'm going to guess that it's 8.2.x, because
8.1.x gets it right :-(.  Try the attached.

            regards, tom lane

Index: planagg.c
===================================================================
RCS file: /cvsroot/pgsql/src/backend/optimizer/plan/planagg.c,v
retrieving revision 1.25
diff -c -r1.25 planagg.c
*** planagg.c    9 Jan 2007 02:14:13 -0000    1.25
--- planagg.c    6 Feb 2007 06:30:23 -0000
***************
*** 70,75 ****
--- 70,76 ----
  optimize_minmax_aggregates(PlannerInfo *root, List *tlist, Path *best_path)
  {
      Query       *parse = root->parse;
+     FromExpr   *jtnode;
      RangeTblRef *rtr;
      RangeTblEntry *rte;
      RelOptInfo *rel;
***************
*** 102,115 ****
       * We also restrict the query to reference exactly one table, since join
       * conditions can't be handled reasonably.  (We could perhaps handle a
       * query containing cartesian-product joins, but it hardly seems worth the
!      * trouble.)
       */
!     Assert(parse->jointree != NULL && IsA(parse->jointree, FromExpr));
!     if (list_length(parse->jointree->fromlist) != 1)
!         return NULL;
!     rtr = (RangeTblRef *) linitial(parse->jointree->fromlist);
!     if (!IsA(rtr, RangeTblRef))
          return NULL;
      rte = rt_fetch(rtr->rtindex, parse->rtable);
      if (rte->rtekind != RTE_RELATION || rte->inh)
          return NULL;
--- 103,121 ----
       * We also restrict the query to reference exactly one table, since join
       * conditions can't be handled reasonably.  (We could perhaps handle a
       * query containing cartesian-product joins, but it hardly seems worth the
!      * trouble.)  However, the single real table could be buried in several
!      * levels of FromExpr.
       */
!     jtnode = parse->jointree;
!     while (IsA(jtnode, FromExpr))
!     {
!         if (list_length(jtnode->fromlist) != 1)
!             return NULL;
!         jtnode = linitial(jtnode->fromlist);
!     }
!     if (!IsA(jtnode, RangeTblRef))
          return NULL;
+     rtr = (RangeTblRef *) jtnode;
      rte = rt_fetch(rtr->rtindex, parse->rtable);
      if (rte->rtekind != RTE_RELATION || rte->inh)
          return NULL;