SELECT statement with sub-queries

Hello *,

I try to get columns from my database with a singel SELECT, but I stuck.

I have 3 tables like:

1) categories (serial,cat)

2) manufacturers (serial,m_name)

3) products (serial,category,manufacturer,p_name)

where the "category" and "manufacturer"
are numerical IDs from the two tables above.

So I like to replace the numerical IDs with the appropriated values,
mean

SELECT * FROM products WHERE category IN
(SELECT categories.cat FROM categories WHERE
categories.serial==products.category);

But I get:

ERROR: operator does not exist: integer==integer
LINE1: ...gories.cat FROM categories WHERE categories.serial==products.category);
^
Hmm, "serial" is an "integer" and the "category" and "manufacturer" too.

So whats wrong with it?

--
Michelle Konzack Miila ITSystems @ TDnet
GNU/Linux Developer 00372-54541400