MySQL查询结果行转列列转行

Posted 2021-11-25 hzh-java

一、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：

 

 

二、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：