The following bug has been logged on the website:
Bug reference: 6662
Logged by: Maxim Boguk
Email address: maxim.boguk@gmail.com
PostgreSQL version: 9.1.3
Operating system: Linux
Description:=20=20=20=20=20=20=20=20
I managed create simple self-contained test case for 6658.
create table test as select * from generate_series(1,100000) as g(val);
create index test_val_special on test((val || ''));
analyze test;
select count(*) from test;
--ok
--index scan
explain analyze
SELECT val
FROM test
WHERE (val || '')=3D'something';
QUERY PLAN
---------------------------------------------------------------------------=
--------------------------------------------
Index Scan using test_val_special on test (cost=3D0.01..8.29 rows=3D1 wid=
th=3D4)
(actual time=3D0.011..0.011 rows=3D0 loops=3D1)
Index Cond: (((val)::text || ''::text) =3D 'something'::text)
Total runtime: 0.038 ms
--not ok
--seq scan on 9.1.3
explain analyze
SELECT val=20
FROM
(
SELECT
val,
(val || '') AS search_string
FROM test
) AS t1
WHERE search_string=3D'something';
QUERY PLAN
---------------------------------------------------------------------------=
---------------------------------------
Subquery Scan on t1 (cost=3D0.00..3443.00 rows=3D500 width=3D4) (actual
time=3D47.076..47.076 rows=3D0 loops=3D1)
Filter: (t1.search_string =3D 'something'::text)
-> Seq Scan on test (cost=3D0.00..2193.00 rows=3D100000 width=3D4) (ac=
tual
time=3D0.012..34.949 rows=3D100000 loops=3D1)
Total runtime: 47.091 ms
--the same second query on 8.3.13
--plan correct
QUERY PLAN
---------------------------------------------------------------------------=
--------------------------------------------
Index Scan using test_val_special on test (cost=3D0.01..8.29 rows=3D1 wid=
th=3D4)
(actual time=3D0.004..0.004 rows=3D0 loops=3D1)
Index Cond: (((val)::text || ''::text) =3D 'something'::text)
Total runtime: 0.018 ms
Kind Regards,
Maksym
