From e9f2703ab7b29f7e9100807cfbd19ddebbaa0b12 Mon Sep 17 00:00:00 2001
From: Tom Lane <tgl@sss.pgh.pa.us>
Date: Fri, 12 Jan 2018 16:52:49 -0500
Subject: Fix postgres_fdw to cope with duplicate GROUP BY entries.

Commit 7012b132d, which added the ability to push down aggregates and
grouping to the remote server, wasn't careful to ensure that the remote
server would have the same idea we do about which columns are the grouping
columns, in cases where there are textually identical GROUP BY expressions.
Such cases typically led to "targetlist item has multiple sortgroupref
labels" errors.

To fix this reliably, switch over to using "GROUP BY column-number" syntax
rather than "GROUP BY expression" in transmitted queries, and adjust
foreign_grouping_ok() to be more careful about duplicating the sortgroupref
labeling of the local pathtarget.

Per bug #14890 from Sean Johnston.  Back-patch to v10 where the buggy code
was introduced.

Jeevan Chalke, reviewed by Ashutosh Bapat

Discussion: https://postgr.es/m/20171107134948.1508.94783@wrigleys.postgresql.org
---
 contrib/postgres_fdw/sql/postgres_fdw.sql | 6 ++++++
 1 file changed, 6 insertions(+)

(limited to 'contrib/postgres_fdw/sql/postgres_fdw.sql')

diff --git a/contrib/postgres_fdw/sql/postgres_fdw.sql b/contrib/postgres_fdw/sql/postgres_fdw.sql
index 3c3c5c705f6..2bdf7d8c1ef 100644
--- a/contrib/postgres_fdw/sql/postgres_fdw.sql
+++ b/contrib/postgres_fdw/sql/postgres_fdw.sql
@@ -636,6 +636,12 @@ explain (verbose, costs off)
 select count(c2) w, c2 x, 5 y, 7.0 z from ft1 group by 2, y, 9.0::int order by 2;
 select count(c2) w, c2 x, 5 y, 7.0 z from ft1 group by 2, y, 9.0::int order by 2;
 
+-- GROUP BY clause referring to same column multiple times
+-- Also, ORDER BY contains an aggregate function
+explain (verbose, costs off)
+select c2, c2 from ft1 where c2 > 6 group by 1, 2 order by sum(c1);
+select c2, c2 from ft1 where c2 > 6 group by 1, 2 order by sum(c1);
+
 -- Testing HAVING clause shippability
 explain (verbose, costs off)
 select c2, sum(c1) from ft2 group by c2 having avg(c1) < 500 and sum(c1) < 49800 order by c2;
-- 
cgit v1.2.3

