Indexes and differing column types

Hi all,

this is my first mail to pgsql-hackers, so first I want to thank you all for
your great work. PostgreSQL is an amazing database management system and
wonderful to use.

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?

Best Regards,
Michael Paesold