Re: BUG #5084: Query gives different number of rows depending on ORDER BY - Mailing list pgsql-bugs

> Bernt Marius Johnsen wrote:
 >> Dump of the database:

To save anyone else the bother, there's a VASTLY simpler testcase for
this one, requiring no tables at all:

test1=# explain select * from (values (1),(null)) v(k) where k = k order by k;
                            QUERY PLAN
-------------------------------------------------------------------
 Sort  (cost=0.04..0.04 rows=2 width=4)
   Sort Key: "*VALUES*".column1
   ->  Values Scan on "*VALUES*"  (cost=0.00..0.03 rows=2 width=4)
(3 rows)

test1=# explain select * from (values (1),(null)) v(k) where k = k;
                         QUERY PLAN
-------------------------------------------------------------
 Values Scan on "*VALUES*"  (cost=0.00..0.03 rows=1 width=4)
   Filter: (column1 = column1)
(2 rows)

Notice that the (k = k) qual is being dropped somewhere, which changes
the output since that's a disguised not-null condition.

--
Andrew (irc:RhodiumToad)