我正在尝试运行一个查询,其中两列不相同,但是没有返回任何结果:
I'm trying to run a query where two columns are not the same, but it's not returning any results:
SELECT * FROM `my_table` WHERE `column_a` != `column_b`;column_a和column_b是整数类型,可以包含空值.我试过使用<> IS NOT等等,没有任何运气.使用< =>可以很容易地找到它们是否相同,但是<>和!=不会返回任何行. (使用Mysql 5.0).
column_a AND column_b are of integer type and can contain nulls. I've tried using <> IS NOT, etc without any luck. It's easy to find if they're the same using <=>, but <> and != doesn't return any rows. (using Mysql 5.0).
有想法吗?
推荐答案问题是当a或b为NULL时,a!= b为NULL.
The problem is that a != b is NULL when either a or b is NULL.
<=> 是NULL安全等于运算符.要获得不等于NULL的安全值,您可以简单地将结果取反:
<=> is the NULL-safe equals operator. To get a NULL-safe not equal to you can simply invert the result:
SELECT * FROM my_table WHERE NOT column_a <=> column_b如果不使用null安全运算符,则必须执行以下操作:
Without using the null safe operator you would have to do this:
SELECT * FROM my_table WHERE column_a != column_b OR (column_a IS NULL AND column_b IS NOT NULL) OR (column_b IS NULL AND column_a IS NOT NULL)更多推荐
Mysql选择行,其中两列不具有相同的值
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