数据库之列转行、行转列

数据库之列转行、行转列

创建表

# 建表语句
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;

添加数据

# 添加数据
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);

列转行 SQL

# 列转行
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;

列转行的变化

行转列

需要先将转换后的数据存入到结果表中result

# 创建表结果表
CREATE TABLE `result` (
  `USER_NAME` varchar(20) DEFAULT NULL,
  `COURSE` varchar(20) DEFAULT NULL,
  `SCORE` float DEFAULT '0'
) ENGINE=InnoDB AUTO_INCREMENT=1 DEFAULT CHARSET=utf8;
# 将查询到的数据转入到结果表中
insert into result
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;

之后再进行行转列

# 行转列
select USER_NAME,'语文' COURSE,MAX(语文) as score from result GROUP by USER_NAME union ALL
select USER_NAME,'数学' COURSE,MAX(数学) as score from result  GROUP by USER_NAME union ALL
select USER_NAME,'英语' COURSE,MAX(英语) as score from result  GROUP by USER_NAME

行转列的变化