行列转换

sql进行行列转换

资源

• MySQL行转列与列转行 （备用）

• https://blog.csdn.net/jx_870915876/java/article/details/52403472

例子

行转列

表结构

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;

数据

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

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;

列转行

表结构

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;

插入数据

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);

列转行sql

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;

备注：

select user_name, '语文' COURSE , CN_SCORE as SCORE from test_tb_grade2 

上面的 ‘语文’ 容易产生误会，实际上，就是拿一个常数值作为字段而已，字段的名称叫COURSE而已。