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查询来实现这一目标：-

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

Answer 1

您应该像...一样运行您的sql查询。

SELECT * from schools 
WHERE `district_id` = 
(SELECT district_id from schools 
    WHERE `school_id` = '0023194'
    AND 
    district_id IS NOT NULL) 
AND district_id IS NOT NULL

district_id不为空防止district_id不为空

Answer 2

似乎您只需要使用IN，如下所示：

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

SQL HERE

Answer 3

您可以使用IN运算符，因为IN运算符允许您在WHERE子句中指定多个值。

IN运算符是多个OR条件的简写。在您的条件下，=仅比较一个条件，但是如果您有此school_id的多个记录，则=无法对其进行评估。

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

如何处理子查询返回null

3 个答案: