原文： http://blog.csdn.net/jx_870915876/article/details/52403472
add by zhj: 本文是以MySQL为例说明的，但其实它适用于所有关系型数据库
例如：把图1转换成图2结果展示
图1
图2
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CREATE TABLE `TEST_TB_GRADE` ( `ID` int(10) NOT NULL AUTO_INCREMENT, `USER_NAME` varchar(20) DEFAULT NULL, `COURSE` varchar(20) DEFAULT NULL, `SCORE` float DEFAULT ‘0‘, PRIMARY KEY (`ID`)) ENGINE=InnoDB AUTO_INCREMENT=1 DEFAULT CHARSET=utf8; |
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insert into TEST_TB_GRADE(USER_NAME, COURSE, SCORE) values("张三", "数学", 34),("张三", "语文", 58),("张三", "英语", 58),("李四", "数学", 45),("李四", "语文", 87),("李四", "英语", 45),("王五", "数学", 76),("王五", "语文", 34),("王五", "英语", 89); |
行转列SQL：
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SELECT user_name , MAX(CASE course WHEN ‘数学‘ THEN score ELSE 0 END ) 数学, MAX(CASE course WHEN ‘语文‘ THEN score ELSE 0 END ) 语文, MAX(CASE course WHEN ‘英语‘ THEN score ELSE 0 END ) 英语FROM test_tb_gradeGROUP BY USER_NAME; |
例如：把图1转换成图3结果展示
图3
列转行SQL：
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select user_name, ‘语文‘ COURSE , CN_SCORE as SCORE from test_tb_grade2union select user_name, ‘数学‘ COURSE, MATH_SCORE as SCORE from test_tb_grade2union select user_name, ‘英语‘ COURSE, EN_SCORE as SCORE from test_tb_grade2order by user_name,COURSE; |
原文：https://www.cnblogs.com/ajianbeyourself/p/9639598.html