$sql_groups = 'SELECT name FROM '.$table_group.' g,'.$table_group_user.' gu WHERE g.c_id '.$course_id.' AND gu.user_id="'.$user_id.'" AND gu.group_id=g.id';
$sql_groups = 'SELECT name FROM '.$table_group.' g,'.$table_group_user.' gu
WHERE g.c_id = '.$course_id.' AND gu.user_id = "'.$user_id.'" AND gu.group_id = g.id';