Essayer de supprimer de plusieurs tables à l'aide de SQL

delete ne peut gérer qu'une seule table à la fois, vous aurez donc besoin de trois instructions :

DELETE FROM upklist 
WHERE  session_id = (SELECT session_id 
                     FROM   usession 
                     WHERE  delete_session_id IS NULL 
                            AND user_id = (SELECT user_id 
                                           FROM   users 
                                           WHERE  REGEXP_LIKE(USER_NAME, 
                                                  'awpeople', 'i'))); 

DELETE FROM projshar 
WHERE  session_id = (SELECT session_id 
                     FROM   usession 
                     WHERE  delete_session_id IS NULL 
                            AND user_id = (SELECT user_id 
                                           FROM   users 
                                           WHERE  REGEXP_LIKE(USER_NAME, 
                                                  'awpeople', 'i'))); 

DELETE FROM usession 
WHERE  session_id = (SELECT session_id 
                     FROM   usession 
                     WHERE  delete_session_id IS NULL 
                            AND user_id = (SELECT user_id 
                                           FROM   users 
                                           WHERE  REGEXP_LIKE(USER_NAME, 
                                                  'awpeople', 'i'))); 

Notez que puisque la requête interne repose sur usersession , vous devez en supprimer le dernier .