Calculate space of clients records

[Anon]

I'm trying to find a way that I can calculate how much space of a database a client is using. For example, if I wanted to limit a user to 1MB worth of documents in a couple of tables. To limit them I must first be able to see how much they are using.

Is there a way to do a query that can give me the amount of space (or characters in) a result of records. (Selecting the clients records is easy, I simply add a WHERE clientID = $clientID).

Thanks a bunch to anyone with ideas on this one.

[Anon]

I forgot to mention I'm using MySQL. But if someone has ideas for this in PostgreSQL as well I'd consider switching.