mysql行转列、列转行

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       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;

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);

       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_grade GROUP BY USER_NAME;

       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;

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);

查询语句：

select user_name, '语文' COURSE , CN_SCORE as SCORE from test_tb_grade2 union select user_name, '数学' COURSE, MATH_SCORE as SCORE from test_tb_grade2 union select user_name, '英语' COURSE, EN_SCORE as SCORE from test_tb_grade2 order by user_name,COURSE;

       结果展示：