The following bug has been logged online:

Bug reference: 2006
Logged by: Atanas Hristov
Email address: atanashristov (AT) hotmail (DOT) com
PostgreSQL version: 8.1 Beta 3
Operating system: FreeBSD 5
Description: queryoptimizer and comparing a primary key of biginteger
and a literal
Details:

foo=# CREATE TABLE foo (id BIGINT, CONSTRAINT foo_pk PRIMARY KEY(id) );



foo=# EXPLAIN ANALYZE SELECT 'foo' FROM foo WHERE id = CAST(0 AS BIGINT);
QUERY PLAN
----------------------------------------------------------------------------
--------------------------------
Index Scan using foo_pk on foo (cost=0.00..4.82 rows=2 width=0) (actual
time=0.113..0.113 rows=0 loops=1)
Index Cond: (id = 0::bigint)



foo=# EXPLAIN ANALYZE SELECT 'foo' FROM foo WHERE id = 0; -- WHY POSTGRES
DOES NOT IMPLICITLY DO CASTING OF THE LITERAL "0" ??????
QUERY PLAN
----------------------------------------------------------------------------
------------------
Seq Scan on foo (cost=0.00..22.50 rows=2 width=0) (actual
time=0.003..0.003 rows=0 loops=1)
Filter: (id = 0)

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"Atanas Hristov" <atanashristov (AT) hotmail (DOT) com> writes:
It works for me:

regression=# EXPLAIN ANALYZE SELECT 'foo' FROM foo WHERE id = 0;
QUERY PLAN
------------------------------------------------------------------------------------------------------------
Index Scan using foo_pk on foo (cost=0.00..4.82 rows=1 width=0) (actual time=0.241..0.241 rows=0 loops=1)
Index Cond: (id = 0)
Total runtime: 0.456 ms
(3 rows)

I don't think you're really testing 8.1. Try "select version()"

regards, tom lane

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TIP 9: In versions below 8.0, the planner will ignore your desire to
choose an index scan if your joining column's datatypes do not
match