SQL SUM函數內使用CASE函數

 

- 實例 -

 

在這個表里進行查詢：

 

 

查詢出如下結果（統計每天的輸贏次數）：

 

 

 

 

- 開始查詢 -

 

首先創建測試表：

CREATE TABLE info( date varchar(255), result varchar(255) );

 

 

插入測試數據：

INSERT INTO info(date,result) VALUES('2015-10-09','win'); INSERT INTO info(date,result) VALUES('2015-10-09','lose'); INSERT INTO info(date,result) VALUES('2015-10-09','win'); INSERT INTO info(date,result) VALUES('2015-10-09','lose'); INSERT INTO info(date,result) VALUES('2015-10-10','win'); INSERT INTO info(date,result) VALUES('2015-10-10','win'); INSERT INTO info(date,result) VALUES('2015-10-10','lose');

 

 

起初用了一種最“簡單粗暴”的方式查了出來：

SELECT info.date,winTable.win,loseTable.lose FROM info LEFT JOIN (SELECT date,COUNT(date) AS win FROM info WHERE result = 'win'
             GROUP BY date) winTable ON winTable.date = info.date LEFT JOIN (SELECT date,COUNT(date) AS lose FROM info WHERE result = 'lose'
             GROUP BY date) loseTable ON loseTable.date = info.date GROUP BY info.date,winTable.win,loseTable.lose ORDER BY info.date;

 這方案絕對可以優化！

 

 

 

 

 

果然，用了SUM函數之后，SQL語句變簡單了，效率也大大提高了！

SELECT date, 　　SUM(case result when 'win' then 1 else 0 end) AS win, SUM(case result when 'lose' then 1 else 0 end) AS lose FROM info GROUP BY date ORDER BY date;

 

 

 

 

測試完了，刪除測試表：

DROP TABLE info;

 

 

 

參考資料：

http://www.yiibai.com/mysql/case-function.html

http://www.cnblogs.com/yazdao/archive/2009/12/09/1620482.html

http://blog.csdn.net/u012531272/article/details/50295397

 

 

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 ficow原創，轉載請注明出處： http://www.cnblogs.com/ficow/p/7723550.html