Mysql之case語句（附帶執行個體）

標籤：

這段時間，做項目做累了，好不容易有點個人的學習時間，利用這個小時，總結一下，最近做統計的時候常用的case語句吧。

結構：case  when… then …end

1.判斷的同時改變其值

eg:

                    select OperatorAccount,

                            case

                                         when CreateTime>‘2016-02-14 16:24:42‘ then ‘after‘

                                         when CreateTime<‘2016-02-14 16:24:42‘ then ‘before‘

                                         else ‘now‘ end stage

                    from log_login order by CreateTime DESC

 

第二種寫法

                    SELECT CallerNumber, CASE IsLocal

                                         WHEN 0 THEN ‘外線‘

                                         WHEN 1 THEN ‘內線‘ END

                    FROM cdr

 

2.拆分一行為多列

eg:

                    SELECT SipAccount, COUNT(1) AS number,IsCheck

                    FROM cdr

                    GROUP BY SipAccount,IsCheck

針對這個統計結果進行拆分（0表示未打分，1代表優秀，2代表合格，3代表不合格）

最終結果如下：

 

所以最終要用到行拆分成三列，語句如下

                    SELECT SipAccount,

                    (CASE IsCheck WHEN 1 THEN number END) youxiu,

                    (CASE IsCheck WHEN 2 THEN number END) hege,

                    (CASE IsCheck WHEN 3 THEN number END) buhege

                    FROM

                    (SELECT SipAccount, COUNT(1) AS number,IsCheck

                    FROM cdr

                    GROUP BY SipAccount,IsCheck) AS a

現在結果是這樣的，你會發現雖然拆成了三列，但是最終結果還不是自己需要的，接下來就需要根據sipaccount來分組的同時對結果進行處理了。語句如下：

                    SELECT sipaccount,

                                         IF(MAX(youxiu) IS NULL,0, MAX(youxiu)) youxiu,

                                         IF(MAX(hege) IS NULL,0, MAX(hege)) hege,

                                         IF(MAX(buhege) IS NULL,0, MAX(buhege)) buhege

                    FROM

                    (SELECT SipAccount,

                                         (CASE IsCheck WHEN 1 THEN number END) youxiu,

                                         (CASE IsCheck WHEN 2 THEN number END) hege,

                                         (CASE IsCheck WHEN 3 THEN number END) buhege

                    FROM

  (SELECT SipAccount, COUNT(1) AS number,IsCheck  FROM cdr  GROUP BY SipAccount,IsCheck) AS a) AS b

                    GROUP BY sipaccount

 最終得到了這個結果。正式我們需要的格式

 

 

Mysql之case語句（附帶執行個體）