On 03/01/2011 07:50 PM, Royce Ausburn wrote:
Hi all,
Got an odd one.
test=# select version();
version
-------------------------------------------------------------------------------------------------------------------------------------------
PostgreSQL 8.4.5 on i386-apple-darwin, compiled by GCC
i686-apple-darwin8-gcc-4.0.1 (GCC) 4.0.1 (Apple Computer, Inc. build 5370),
32-bit
(1 row)
test=# create temp table test1 (something integer); CREATE TABLE
test=# create temp table test2 (id1 integer, charge numeric); CREATE TABLE
test=# select * from test2 where id1 in (select id1 from test1) and charge=0.05;
id1 | charge
-----+--------
(0 rows)
Notice the last query's subselect is selecting "id1" from test1, but there's no
such column on id1. Postgres correctly fails when you do:
test=# select id1 from test1;
ERROR: column "id1" does not exist
LINE 1: select id1 from test1;
The plan for the query that I think should have failed:
test=# explain select * from test2 where id1 in (select id1 from test1) and
charge=0.05; QUERY PLAN
-----------------------------------------------------------------
Seq Scan on test2 (cost=0.00..24628.45 rows=3 width=36)
Filter: ((charge = 0.05) AND (SubPlan 1))
SubPlan 1
-> Seq Scan on test1 (cost=0.00..34.00 rows=2400 width=0)
(4 rows)
Notice the sub plan doesn't actually cause any filtering.
This produces incorrect results when there's data in the table:
test=# insert into test1 select 5;
INSERT 0 1
test=# insert into test2 select 10, 70;
INSERT 0 1
test=# select * from test2 where id1 in (select id1 from test1) and charge=70;
id1 | charge
-----+--------
10 | 70
(1 row)
test=# explain select * from test2 where id1 in (select id1 from test1) and
charge=70;
QUERY PLAN
-----------------------------------------------------------------
Seq Scan on test2 (cost=0.00..24628.45 rows=3 width=36)
Filter: ((charge = 70::numeric) AND (SubPlan 1))
SubPlan 1
-> Seq Scan on test1 (cost=0.00..34.00 rows=2400 width=0)
(4 rows)
Am I correct in thinking this is a bug in pg?
--Royce
--Royce
Chief Engineer @ Inomial
03 9999 3125
0417 954 640
Its getting id1 from the parent table. (test2) You can use fields from the
parent table in subselects.
try this and it'll complain:
select * from test2 where id1 in (select junk from test1) and charge=70;
try:
select * from test2 where id1 in (select something from test1 where something =
id1) and charge=70;
-Andy
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