如何在 MySQL 中检查字段是否为空或为空? [英] How to check if field is null or empty in MySQL?

问题描述

我想弄清楚如何检查一个字段是 NULL 还是 empty.我有这个:

I am trying to figure out how to check if a field is NULL or empty. I have this:

SELECT IFNULL(field1, 'empty') as field1 from tablename

我需要添加一个额外的检查 field1 != "" 类似于:

I need to add an additional check field1 != "" something like:

SELECT IFNULL(field1, 'empty') OR field1 != ""  as field1 from tablename

知道如何做到这一点吗?

Any idea how to accomplish this?

推荐答案

要么使用

SELECT IF(field1 IS NULL or field1 = '', 'empty', field1) as field1 
from tablename

或

SELECT case when field1 IS NULL or field1 = ''
            then 'empty'
            else field1
       end as field1 
from tablename

如果您只想检查 null 而不是空字符串，那么您也可以使用 ifnull() 或 coalesce(field1, 'empty').但这不适用于空字符串.

If you only want to check for null and not for empty strings then you can also use ifnull() or coalesce(field1, 'empty'). But that is not suitable for empty strings.

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