Error when executing query:

select * from users where id_user =
with the next error message

You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near '' at line 1
PHP Notice: Undefined index: id_user in D:\websites\thegreatnortherndeli.co.uk\site_backup\frontend\myprofile.php on line 3 PHP Notice: Use of undefined constant id_user - assumed 'id_user' in D:\websites\thegreatnortherndeli.co.uk\site_backup\frontend\myprofile.php on line 4