COALESCE()用于空白(但不为空)字段 [英] COALESCE() for blank (but not null) fields

问题描述

我要与MySQL函数进行比较的两个字段

I have two fields that I'm comparing with MySQL's function COALESCE(). For example, COALESCE(Field1, Field2). The problem is, Field1 is sometimes blank but not null; since it's not null COALESCE() selects Field1, even though its blank. In that case, I need it to select Field2.

我知道我可以在查询中编写if-then-else(CASE)语句来检查这一点，但是是否有像COALESCE()这样的简单函数可以用于空白但非空字段?

I know I can write a if-then-else (CASE) statement in the query to check for this, but is there a nice simple function like COALESCE() for blank-but-not-null fields?

推荐答案

SELECT IFNULL(NULLIF(Field1,''),Field2)

如果Field1为空，则NULLIF返回NULL，如果IFNULL不为空或NULL，则IFNULL返回Field1，否则返回Field2.

NULLIF returns a NULL if Field1 is blank, while IFNULL returns Field1 if it's not blank or NULL and Field2 otherwise.

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