函数详解
- 五月 25, 2019
- 澳门新蒲京娱乐
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mysql中代表null的IFNULL()与COALESCE()函数详解,ifnullcoalesce
澳门新蒲京娱乐 ,在MySQL中isnull()
函数不可能看做代表null值!
如下:
首先有个名为business的表:
SELECT ISNULL(business_name,'no business_name') AS bus_isnull FROM business WHERE id=2
直接运维就能够报错:
错误代码: 15八二
Incorrect parameter count in the call to native function 'isnull'
所以,isnull()
函数在mysql中就不算了。能够用ifnull()
和coalesce()
代替。如下:
使用ifnull()
函数:
SELECT IFNULL(business_name,'no business_name') AS bus_ifnull FROM business WHERE id=2
运行结果:
当查问的值不为null时:
SELECT IFNULL(business_name,'no business_name') AS bus_ifnull FROM business WHERE id=1
结果如下:
使用coalesce()
函数:
SELECT COALESCE(business_name,'no business_name') AS bus_coalesce FROM business WHERE id=2
结果如下:
当查问值不为null时:
SELECT COALESCE(business_name,'no business_name') AS bus_coalesce FROM business WHERE id=1
其中:coalesce()
还能回到第九个不为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中怎么用吧?答案就是用在where后边。如下:
SELECT * FROM business WHERE ISNULL(business_name)
结果如下:
同样,is null
和is not null
也是用在where前面。
SELECT * FROM business WHERE business_name IS NULL
结果如下:
SELECT * FROM business WHERE business_name IS NOT NULL
总结
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在MySQL中 isnull() 函数无法同日而语取代null值! 如下:
首先有个名叫business的表: SEL…
mysql中代表null的IFNULL()与COALESCE()函数详解
在MySQL中isnull()函数不可能看做代表null值!
如下: mysql中代表null的IFNULL()与COALESCE()函数详解
首先有个名称叫business的表:
SELECT ISNULL(business_name,’no business_name’) AS bus_isnull
FROM business WHERE id=2
直接运营就能够报错:
错误代码: 158二
Incorrect parameter count in the call to native function ‘isnull’
所以,isnull()函数在mysql中就不算了。能够用ifnull()和coalesce()取代。如下:
使用ifnull()函数:
SELECT IFNULL(business_name,’no business_name’) AS bus_ifnull
FROM business WHERE id=2
运转结果:
当查问的值不为null时:
SELECT IFNULL(business_name,’no business_name’) AS bus_ifnull
FROM business WHERE id=1
结果如下:
使用coalesce()函数:
SELECT COALESCE(business_name,’no business_name’) AS bus_coalesce
FROM business WHERE id=2
结果如下:
当查问值不为null时:
SELECT COALESCE(business_name,’no business_name’) AS bus_coalesce
FROM business WHERE id=1
个中:coalesce()还足以回到第2个不为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中怎么用啊?答案正是用在where后边。如下:
SELECT * FROM business WHERE ISNULL(business_name)
结果如下:
同样,is null 和is not null 也是用在where前边。
SELECT * FROM business WHERE business_name IS NULL
结果如下:
SELECT * FROM business WHERE business_name IS NOT NULL
mysql中代表null的IFNULL()与COALESCE()函数详解
在MySQL中isnull()函数不可能同日而语代表null值! 如下:
mysql中代表null的IFNULL()与COALESCE()函数详解 首先有个…
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