mysql中IFNULL()和COALESCE()函數替代null

在mysql中isnull()函數不能作為替代null值！
如下：
首先有個名字為business的表：

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

直接運行就會報錯：

錯誤代碼： 1582 Incorrect parameter count in the call to native function 'isnull'

所以，isnull()函數在mysql中就行不通了。可以用ifnull()和coalesce()代替。如下：
使用ifnull()函數：

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

運行結果：

當查詢的值不為null時：

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

結果如下：

使用coalesce()函數：

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

結果如下：

當查詢值不為null時：

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

結果如下：

SELECT * FROM business WHERE business_name IS NOT NULL