Mine favoritt-treninger

Error: SELECT s.*, c.name AS category_name, c.icon AS category_icon, c.color AS category_color, u.name AS instructor_name FROM video_session s, video_category c, users u, video_user_session_favorite fav WHERE fav.session_id = s.session_id AND fav.user_id = AND s.category_id = c.category_id AND s.instructor_id = u.user_id AND (s.live = 0 OR s.live = 2) ORDER BY fav.favorite_time DESC

ERROR: syntax error at or near "AND" LINE 1: ... fav.session_id = s.session_id AND fav.user_id = AND s.cate... ^