mysql行转列、列转行

   语句不难，不做多余解释了，看语句时，从内往外一句一句剖析

行转列

       有如图所示的表，现在希望查询的结果将行转成列

       建表语句如下：

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);
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       查询语句：

       此处用之所以用MAX是为了将无数据的点设为0，防止出现NULL

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;
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       结果展示：

列转行

       有如图所示的表，现在希望查询的结果将列成行

       建表语句如下：

CREATE TABLE `TEST_TB_GRADE2` (  `ID` int(10) NOT NULL AUTO_INCREMENT,  `USER_NAME` varchar(20) DEFAULT NULL,  `CN_SCORE` float DEFAULT NULL,  `MATH_SCORE` float DEFAULT NULL,  `EN_SCORE` float DEFAULT '0',  PRIMARY KEY (`ID`)) ENGINE=InnoDB AUTO_INCREMENT=1 DEFAULT CHARSET=utf8;
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insert into TEST_TB_GRADE2(USER_NAME, CN_SCORE, MATH_SCORE, EN_SCORE) values("张三", 34, 58, 58),("李四", 45, 87, 45),("王五", 76, 34, 89);
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查询语句：

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;
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       结果展示：