mysql中替代null的IFNULL()與COALESCE()函數(shù)詳細(xì)說明_Mysql

在MySQL中isnull()函數(shù)不能作為替代null值！

如下：

首先有個(gè)名字為business的表：

SELECT ISNULL(business_name,'no business_name') AS bus_isnull FROM business WHERE id=2

直接運(yùn)行就會(huì)報(bào)錯(cuò)：

錯(cuò)誤代碼： 1582

Incorrect parameter count in the call to native function 'isnull'

所以，isnull()函數(shù)在mysql中就行不通了�？梢杂�ifnull()和coalesce()代替。如下：

使用ifnull()函數(shù)：

SELECT IFNULL(business_name,'no business_name') AS bus_ifnull FROM business WHERE id=2

運(yùn)行結(jié)果：

當(dāng)查詢的值不為null時(shí)：

SELECT IFNULL(business_name,'no business_name') AS bus_ifnull FROM business WHERE id=1

結(jié)果如下：

使用coalesce()函數(shù)：

SELECT COALESCE(business_name,'no business_name') AS bus_coalesce FROM business WHERE id=2

結(jié)果如下：

當(dāng)查詢值不為null時(shí)：

SELECT COALESCE(business_name,'no business_name') AS bus_coalesce FROM business WHERE id=1

其中：coalesce()還可以返回第一個(gè)不為null的值。如下：

SELECT COALESCE(business_name,district_id,id) AS bus_coalesce FROM business WHERE id=2

那么，isnull()在mysql中怎么用呢？答案就是用在where后面。如下：

SELECT * FROM business WHERE ISNULL(business_name)

結(jié)果如下：

同樣，is null 和is not null 也是用在where后面。

SELECT * FROM business WHERE business_name IS NULL

結(jié)果如下：

SELECT * FROM business WHERE business_name IS NOT NULL

總結(jié)

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