MySQL列名称和别名 [英] MySQL column names and aliases

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本文介绍了MySQL列名称和别名的处理方法,对大家解决问题具有一定的参考价值,需要的朋友们下面随着小编来一起学习吧!

问题描述

我已经阅读到选择后我们使用列名,但是我发现了一条类似这样的语句:

I have read that after select we use column-names but I have found a statement that was like this:

SELECT 'A' FROM T WHERE A = NULL;

你愿意帮我吗?谢谢(这里是列名吗?) 我的DBMS是MySQL

would you lease help me? thanks (A is a column- name here?) my DBMS is MySQL

确切的问题是这样的: 上面的语句是否会产生一行(选择所有 申请)?请注意,ANSI_NULLS为OFF.

EDITED : the exact question is this that: Will the above statement produce a row (select all that apply)? Notice that ANSI_NULLS is OFF.

我想知道上面的陈述会奏效吗?因为有些人说我们应该写IS NULL而不是= null

I want to know that the above statement will work? because some of you said that we should write IS NULL instead of =null

推荐答案

基于该查询,对于名为A的列等于null的每一行,您将获得一个包含字符'A'的结果集.

Based on that query, you would get a result set containing the character 'A' for each row where the column named A was equal to null.

如果您实际上想查看A列的值而不是字符"A",则必须删除单引号:

If you actually want to see the value of the column A instead of the character 'A', you have to remove the single quotes:

SELECT A FROM T WHERE A IS NULL

无论哪种方式,都不应该使用= NULL.某些RDMS无法按照您的想法进行处理.标准是使用IS NULL代替.

Either way, you should not use = NULL. Certain RDMSs don't handle that the way you would think. The standard is to use IS NULL instead.

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