Fix case of window function + aggregate + GROUP BY expression.

In commit 1bc16a946008a7cbb33a9a06a7c6765a807d7f59 I added a minor
optimization to drop the component variables of a GROUP BY expression from
the target list computed at the aggregation level of a query, if those Vars
weren't referenced elsewhere in the tlist.  However, I overlooked that the
window-function planning code would deconstruct such expressions and thus
need to have access to their component variables.  Fix it to not do that.

While at it, I removed the distinction between volatile and nonvolatile
window partition/order expressions: the code now computes all of them
at the aggregation level.  This saves a relatively expensive check for
volatility, and it's unclear that the resulting plan isn't better anyway.

Per bug #7535 from Louis-David Mitterrand.  Back-patch to 9.2.

2 files changed, 18 insertions, 0 deletions

diff --git a/src/test/regress/expected/window.out b/src/test/regress/expected/window.out
index 77786266255..49252c82ae3 100644
--- a/src/test/regress/expected/window.out
+++ b/src/test/regress/expected/window.out
@@ -614,6 +614,18 @@ group by ten order by ten;
    9 | 10040184 |    7
 (10 rows)
 
+-- window and aggregate with GROUP BY expression (9.2 bug)
+explain (costs off)
+select first_value(max(x)) over (), y
+  from (select unique1 as x, ten+four as y from tenk1) ss
+  group by y;
+          QUERY PLAN           
+-------------------------------
+ WindowAgg
+   ->  HashAggregate
+         ->  Seq Scan on tenk1
+(3 rows)
+
 -- test non-default frame specifications
 SELECT four, ten,
 	sum(ten) over (partition by four order by ten),
diff --git a/src/test/regress/sql/window.sql b/src/test/regress/sql/window.sql
index d8e9e7e3b1c..769be0fdc61 100644
--- a/src/test/regress/sql/window.sql
+++ b/src/test/regress/sql/window.sql
@@ -145,6 +145,12 @@ select ten,
 from tenk1
 group by ten order by ten;
 
+-- window and aggregate with GROUP BY expression (9.2 bug)
+explain (costs off)
+select first_value(max(x)) over (), y
+  from (select unique1 as x, ten+four as y from tenk1) ss
+  group by y;
+
 -- test non-default frame specifications
 SELECT four, ten,
 	sum(ten) over (partition by four order by ten),