Row level security

[Martin King-Turner]

Is it possible to restrict access to rows in a table, based on data contained in the row?

Here's an example. I have a table which contains messages for individual users. To keep it simple, let's say I have just 2 columns - userid and message. I would like to setup the security so that when a particular user tries to access the table (even with a SELECT * query), they will be able to see *only* those rows where the value of the data in the userid column is equal to their MySQL login.

Any ideas on how to achieve this would be gratefully received.

Thanks,
Martin