MySQL的IFNULL ELSE [英] mysql IFNULL ELSE
问题描述
我有一条select语句,我想在其中选择条件,
I have a select statement where I want to make select conditional like this
IFNULL(field_a,field_a,feild_b)
以便它检查字段a如果a为空,则选择字段为b
so that it checks field a if a is null then the select would be field b
那有可能吗?
推荐答案
使用凉粉:
SELECT COALESCE(field_a, field_b)
COALESCE是ANSI标准函数,它从指定的列列表中返回第一个非空值,并从左到右处理这些列.因此,在示例中,如果field_a
为null,则将显示field_b
值.但是,如果指定的列中没有非空值,则此函数将返回NULL.
COALESCE is an ANSI standard function that returns the first non-null value from the list of columns specified, processing the columns from left to right. So in the example, if field_a
is null, field_b
value will be displayed. However, this function will return NULL if there is no non-null value from the columns specified.
它在MySQL(我在4.1上使用过),SQL Server(从v2000开始),Oracle 9i +上受支持.
It's supported on MySQL (I've used it on 4.1), SQL Server (since v2000), Oracle 9i+...
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