Re: Indexes and differing column types

I wrote:

> Concerning this TODO entry:
>
> > Allow SELECT * FROM tab WHERE int2col = 4 to use int2col index,
> > int8, float4, numeric/decimal too [optimizer]
>
> What about the case of doing a join on columns that don't have the same
> type? Sometimes the index will be used, e.g. on this simple query:
>
> SELECT * FROM a, b WHERE a.int4col = b.int8col;
>
> Here the index will be used. But there are other queries where it's
> necessary to do explicit type casting. I could provide examples.
> Is this a known problem?

I am sorry, the problem is not with joins but with subqueries.

SELECT a.*, (SELECT max(b.someval) FROM b WHERE b.int8val = a.int4val) FROM
a;
-->
QUERY PLAN:
Seq Scan on a (cost=0.00..60.37 rows=2237 width=128)
SubPlan
-> Seq Scan on b (cost=0.00..373.76 rows=1 width=4)

SELECT a.*, (SELECT max(b.someval) FROM b WHERE b.int8val = a.int4val::int8)
FROM a;
-->
QUERY PLAN:
Seq Scan on a (cost=0.00..60.37 rows=2237 width=128)
SubPlan
-> Index Scan using b_pkey on b (cost=0.00..2.04 rows=1 width=4)

Regards, Michael