Help needed about queries with MySQL, thanks.

Hello everyone, I am a new PHP user, from Belgium. I am trying to manage a MySQL database with PHP, and I kindly request your help to solve a little (probably very stupid) problem I have been dealing with for a while already ... I have a MySQL database (called "sessions") with a auto-increment INT field called "sessionID". I try to check if there is already a record in this database with a given sessionID, which is called $sessionID in PHP. I use this query, which must be wrong (but I cannot find out why !!!) : SELECT * FROM sessions WHERE sessionID = $sessionID Even though there is already a record with the right sessionID, my program does not find it (I always get 0 when using mysql_num_rows() after the query). Though, if I replace "$sessionID" by, for example 4, then that works and it says there is already a record with that ID. I guess the problem comes from comparing two different kinds of variables, but I can't fix it ... Could anyone please help ? By advance, thank you !!! Best regards from Belgium, Jean-marc