SQL Help - multi values

Hello

I've just posted this question on the MySQL list but as I'm thinking of moving
to PostGresQL I thought I'd post to this list too... Hope someone can help!

Basically the problem I am having is how best to handle multiple values for
a specific column, in this case the values in question are coming from an
HTML SELECT MULTI box processed by PHP.

The way I have been doing this so far is to have a delimited value stored
in a varchar column, e.g. If my select box returns the values 2,4 and 7 I

insert into my table the string '|2|4|7|'.

Surely there must be a better way than this - but it escapes me. In this
setup the only way to match a specifc value when searching is to use the query:
SELECT dataid,title FROM table WHERE category LIKE '%|4|%'
Which obviously has a huge performance penalty - and of course you can't
JOIN against any of these values.

The only other way I thought of was to use a separate table for the
category entries:

SELECT dataid,title,category FROM table LEFT JOIN table_categories ON
table.dataid=table_categories.dataid

But in the example above this would return 3 entries, which I don't want,
and I can't select a particular dataid which satisfies more than category,
e.g. has categories 4 and 7 (i.e. for the example above the LIKE statement
would be: WHERE category LIKE '%|4|%' AND LIKE '%|7|%').

Any ideas? Please help!

Cheers,

james