带有NULL字段的mysql联合 [英] mysql union with NULL fields

问题描述

mysql UNION和UNION ALL运算符是否总是删除其中包含NULL的行吗?

Does the mysql UNION and UNION ALL operator always remove rows that have a NULL in them?

我正在执行两个SELECT语句的UNION-其中一个可能返回其中包含NULL的行.如果这样做的话，它就不会在UNION中包含该行.有办法解决吗?

I am doing a UNION of two SELECT statements - one of which may return a row with a NULL in it. When it does, it does not include that row in the UNION. Is there a way around this?

推荐答案

UNION/UNION ALL不会删除其中包含NULL的行.

The UNION/UNION ALL does not remove rows with NULL in them.

UNION删除重复的行； UNION ALL不会，并且比UNION快.

UNION removes duplicate rows; UNION ALL does not, and is faster than UNION for it.

检查您的数据&查询您为什么看不到空值的原因.

Check your data & your query for why NULLs you expect to see are not visible.

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