mysql - 如何处理子查询返回null

Question

如果子选择不为空，我只想运行父选择。不确定如何使用 sql 查询实现此目的:-

SELECT * from schools 
    WHERE `district_id` =
    (SELECT district_id from schools WHERE `school_id` = '0023194')

Answer 1

看来你只需要像下面这样使用 IN :

SELECT * from schools 
WHERE `district_id` in
(SELECT district_id from schools WHERE `school_id` = '0023194')

SQL HERE