查询家长和小孩姓名，通过学籍号关联

SELECT a.user_id AS parent_id,a.student_num AS parent_num, a.realname AS parent_name, stu.user_id AS child_id, stu.student_num AS stu_num, stu.realname AS child_nameFROM (SELECT     user_id,student_num, realname  FROM    jc_user_ext e   WHERE e.zone_id = 1     AND e.is_disabled = 0    AND e.user_type_num = 3   ) aLEFT JOIN   (SELECT     user_id,student_num, realname  FROM    jc_user_ext e   WHERE e.zone_id = 1     AND e.is_disabled = 0    AND e.user_type_num = 1      AND e.student_num IS NOT NULL ) stu ON a.student_num=stu.student_num 

userid | 家长姓名 | 小孩姓名

家长id | 张三他爸 | 张三