如何处理子查询返回空值
如何处理子查询返回空值
提问于 2018-08-01 02:01:20
我只想在子选择不为空的情况下运行父选择。不确定如何使用sql查询实现这一点：
SELECT * from schools
WHERE `district_id` =
(SELECT district_id from schools WHERE `school_id` = '0023194')回答 3
Stack Overflow用户
发布于 2018-08-01 02:13:40
看起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
Stack Overflow用户
发布于 2018-08-01 02:06:33
您应该像这样运行您的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 NULLdistrict_id不为空以防止district_id不为空
Stack Overflow用户
发布于 2018-08-01 02:35:16
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，=只比较一个条件，但是如果您有此school_id的多个记录，=将无法对其求值。
SELECT * from schools WHERE `district_id` in (SELECT district_id from schools WHERE `school_id` = '0023194')页面原文内容由Stack Overflow提供。腾讯云小微IT领域专用引擎提供翻译支持
原文链接：
https://stackoverflow.com/questions/51619445
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