mysql的行转列和列转行

行转列

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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_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 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 grade
GROUP BY user_name;

结果展示：

列转行

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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 `grade` (
`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 grade(`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 grade
union select user_name, '数学' COURSE, MATH_SCORE as SCORE from grade
union select user_name, '英语' COURSE, EN_SCORE as SCORE from grade
order by user_name,COURSE;

结果展示：