MySQL 行转列与列传行的使用

一、MySQL版本

• MySQL版本 8.0.11

二、行转列

1.行转列 方法一

1.1 建表语句

-- 建表语句
CREATE TABLE `student` (
  `id` int(7) NOT NULL COMMENT '学号',
  `stu_name` varchar(20) NOT NULL COMMENT '学生姓名',
  `course_name` varchar(100) NOT NULL COMMENT '课程名称',
  `score` float DEFAULT NULL COMMENT '分数',
  PRIMARY KEY (`id`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_0900_ai_ci;

-- 插入数据
insert  into `student`(`id`,`stu_name`,`course_name`,`score`) values 
(1,'张三','数学',67),
(2,'张三','语文',88),
(3,'张三','英语',91),
(4,'李四','数学',73),
(5,'李四','语文',79),
(6,'李四','英语',82),
(7,'王五','数学',95),
(8,'王五','语文',91),
(9,'王五','英语',63),
(10,'赵六','数学',84),
(11,'赵六','语文',89),
(12,'赵六','英语',80),
(13,'田七','数学',77),
(14,'田七','语文',81),
(15,'田七','英语',92),
(16,'周八','数学',50),
(17,'周八','语文',42),
(18,'周八','英语',62);

1.2 数据展示

1.3 编写SQL

SELECT
    stu_name ,
    MAX(CASE course_name WHEN '数学' THEN score ELSE NULL END) '数学1',
    MAX(CASE course_name WHEN '语文' THEN score ELSE NULL END) '语文1',
    MAX(CASE course_name WHEN '英语' THEN score ELSE NULL END) '英语1'
FROM 
	student 
GROUP BY 
	stu_name ;

1.4 执行结果

1.5 计算个人总分数和每门课程平均分数

• 计算个人总分数 和 每门课程平均分数

1.5.1 WITH ROLLUP + sum() 方法一

• 先查询出个人总分数作为子表，然后行转列操作计算每门课程的平均分
• 编写SQL

SELECT
	IFNULL( stu_name, '平均分(方式一)' ) stu_name,
	FORMAT( AVG( CASE course_name WHEN '数学' THEN score ELSE NULL END ), 2 ) '数学1',
	FORMAT( AVG( CASE course_name WHEN '语文' THEN score ELSE NULL END ), 2 ) '语文1',
	FORMAT( AVG( CASE course_name WHEN '英语' THEN score ELSE NULL END ), 2 ) '英语1',
	SUM( CASE course_name WHEN 'selfTotal' THEN score ELSE NULL END ) 'selfTotal' 
FROM
	(
SELECT
	stu_name,
	IFNULL( course_name, 'selfTotal' ) course_name,
	SUM( score ) score 
FROM
	student 
GROUP BY
	stu_name,
	course_name WITH ROLLUP 
HAVING
	stu_name IS NOT NULL 
	) t1 
GROUP BY
	stu_name WITH ROLLUP

• 执行结果：
  

1.5.2 UNION + sum() 方法二

• 编写SQL

SELECT
	IFNULL( stu_name, '平均分(方式二)' ) stu_name,
	SUM( CASE course_name WHEN '数学' THEN score ELSE NULL END ) '数学1',
	SUM( CASE course_name WHEN '语文' THEN score ELSE NULL END ) '语文1',
	SUM( CASE course_name WHEN '英语' THEN score ELSE NULL END ) '英语1',
	SUM( score ) 'selfTotal' 
FROM
	student 
GROUP BY
	stu_name UNION
SELECT
	'平均分(方式二)',
	FORMAT( AVG( CASE course_name WHEN '数学' THEN score ELSE NULL END ), 2 ) '数学1',
	FORMAT( AVG( CASE course_name WHEN '语文' THEN score ELSE NULL END ), 2 ) '语文1',
	FORMAT( AVG( CASE course_name WHEN '英语' THEN score ELSE NULL END ), 2 ) '英语1',
	SUM( score ) 'selfTotal' 
FROM
	student

• 执行结果
  

1.5.2 直接使用sum()，不再使用子查询 方法三

• 编写SQL

SELECT
	IFNULL( stu_name, '平均分(方式三)' ) AS stu_name,
	FORMAT( AVG( CASE course_name WHEN '数学' THEN score ELSE NULL END ), 2 ) '数学1',
	FORMAT( AVG( CASE course_name WHEN '语文' THEN score ELSE NULL END ), 2 ) '语文1',
	FORMAT( AVG( CASE course_name WHEN '英语' THEN score ELSE NULL END ), 2 ) '英语1',
	SUM( score ) AS selfTotal 
FROM
	student 
GROUP BY
	stu_name WITH ROLLUP;

• 执行结果
  

2.行转列 方法二

2.1 编写SQL

SELECT DISTINCT
	t2.stu_name,
	( SELECT score FROM student t1 WHERE t1.stu_name = t2.stu_name AND t1.course_name = '数学' ) AS '数学2',
	( SELECT score FROM student t1 WHERE t1.stu_name = t2.stu_name AND t1.course_name = '语文' ) AS '语文2',
	( SELECT score FROM student t1 WHERE t1.stu_name = t2.stu_name AND t1.course_name = '英语' ) AS '英语2' 
FROM
	student t2;

2.2 执行结果

3.行转列 方法三

• 不再使用 case…when…then…else…end语法，直接使用if()

3.1 编写SQL

SELECT
	stu_name,
	SUM( IF ( course_name = '数学', score, 0 ) ) AS '语文3',
	SUM( IF ( course_name = '语文', score, 0 ) ) AS '数学3',
	SUM( IF ( course_name = '英语', score, 0 ) ) AS '英语3' 
FROM
	student 
GROUP BY
	stu_name

3.2执行结果

三、列转行

3.1 建表语句

-- 建表语句
CREATE TABLE `student1` (
  `id` int(5) NOT NULL AUTO_INCREMENT COMMENT '主键',
  `stu_name` varchar(32) DEFAULT NULL COMMENT '学生名称',
  `language` varchar(32) DEFAULT NULL COMMENT '语文',
  `math` varchar(32) DEFAULT NULL COMMENT '数学',
  `english` varchar(32) DEFAULT NULL COMMENT '英语',
  PRIMARY KEY (`id`)
) ENGINE=InnoDB AUTO_INCREMENT=6 DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_0900_ai_ci;
-- 插入数据
insert  into `student1`(`id`,`stu_name`,`language`,`math`,`english`) values 
(1,'张三','67','88','91'),
(2,'李四','73','79','82'),
(3,'王五','95','91','63'

3.2 数据展示

3.3 编写SQL

SELECT stu_name,'语文' AS course_name,LANGUAGE AS score FROM student1
UNION ALL
SELECT stu_name,'数学' AS course_name,math AS score FROM student1
UNION ALL
SELECT stu_name,'英语' AS course_name,english AS score FROM student1
ORDER BY stu_name

3.4 执行结果

• 执行结果：