澳门新蒲京娱乐


pt-query-digest(percona toolkit)小解,ptquerydigest

数据中心规划,数据中心运营计划的基本原则

函数详解

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:

澳门新蒲京娱乐 1

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()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:

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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:

澳门新蒲京娱乐 3

使用coalesce()函数:

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

结果如下:

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当查问值不为null时:

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

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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

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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:

澳门新蒲京娱乐 7

同样,is nullis not null也是用在where前面。

SELECT * FROM business WHERE business_name IS NULL

结果如下:

澳门新蒲京娱乐 8

SELECT * FROM business WHERE business_name IS NOT NULL

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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:

澳门新蒲京娱乐 10

  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:

澳门新蒲京娱乐 11

  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:

澳门新蒲京娱乐 12

  使用coalesce()函数:

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

  结果如下:

澳门新蒲京娱乐 13

  当查问值不为null时:

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

澳门新蒲京娱乐 14

  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

澳门新蒲京娱乐 15

  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:

澳门新蒲京娱乐 16

  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:

澳门新蒲京娱乐 17

  SELECT * FROM business WHERE business_name IS NOT NULL
  mysql中代表null的IFNULL()与COALESCE()函数详解

澳门新蒲京娱乐 18

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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