verify data in fields

My mysql table contains data. But I don't know how to verify what exactly is the data... is it an array, an integer, an alphanumeric character or what? vardump($whatever) returns null; the structure of the table is no null for the column fields and has been filled like this: $autoid = 1; $test = $_POST['categoriesIN']; // this can be several selections from form $tstring = implode(',' , $test); echo $tstring.'<br />'; $insert_category = "INSERT INTO book_categories (book_id, categories_id) VALUES ($autoid, $tstring.)"; mysql_query($insert_category,$db); retrieval of data is: from SELECT ...snip... LEFT JOIN book_publisher as abc ON b.id = abc.bookID LEFT JOIN publishers AS c ON abc.publishers_id = c.id LEFT JOIN book_categories AS d ON b.id = d.book_id LEFT JOIN categories AS e ON d.categories_id = e.id I have included the publisher stuff - it works, whereas the category stuff does not... -- unheralded genius: "A clean desk is the sign of a dull mind. " ------------------------------------------------------------- Phil Jourdan --- pj@ptahhotep.com http://www.ptahhotep.com http://www.chiccantine.com/andypantry.php