MySQL 搞定行转列，列转行

行转列方法总结

1、使用case…when…then

2、使用SUM(IF()) 生成列

3、使用SUM(IF()) 生成列 + WITH ROLLUP 生成汇总行

4、使用SUM(IF()) 生成列 + UNION 生成汇总行,并利用 IFNULL将汇总行标题显示为 Total

5、使用SUM(IF()) 生成列，直接生成汇总结果，不再利用子查询

环境准备：建表语句 + 初始化数据

-- house.base_score definition

CREATE TABLE `base_score` (
  `id` int NOT NULL AUTO_INCREMENT,
  `userid` varchar(20) NOT NULL COMMENT '用户id',
  `subject` varchar(20) DEFAULT NULL COMMENT '科目',
  `score` double DEFAULT NULL COMMENT '成绩',
  PRIMARY KEY (`id`)
) ENGINE=InnoDB AUTO_INCREMENT=11 DEFAULT CHARSET=utf8;

--- 插入数据

INSERT INTO base_score(userid,subject,score) VALUES ('001','语文',90);
INSERT INTO base_score(userid,subject,score) VALUES ('001','数学',92);
INSERT INTO base_score(userid,subject,score) VALUES ('001','英语',80);
INSERT INTO base_score(userid,subject,score) VALUES ('002','语文',88);
INSERT INTO base_score(userid,subject,score) VALUES ('002','数学',90);
INSERT INTO base_score(userid,subject,score) VALUES ('002','英语',75.5);
INSERT INTO base_score(userid,subject,score) VALUES ('003','语文',70);
INSERT INTO base_score(userid,subject,score) VALUES ('003','数学',85);
INSERT INTO base_score(userid,subject,score) VALUES ('003','英语',90);
INSERT INTO base_score(userid,subject,score) VALUES ('003','政治',82);

使用case…when…then 实现行转列

-- 通过case...when...then 实现行记录转列记录
SELECT userid,
SUM(CASE `subject` WHEN '语文' THEN score ELSE 0 END) as '语文',
SUM(CASE `subject` WHEN '数学' THEN score ELSE 0 END) as '数学',
SUM(CASE `subject` WHEN '英语' THEN score ELSE 0 END) as '英语',
SUM(CASE `subject` WHEN '政治' THEN score ELSE 0 END) as '政治'
FROM base_score
GROUP BY userid

使用SUM(IF()) 生成行转列

-- 使用sum(if) 实现行记录转列记录
SELECT userid,
SUM(IF(`subject`='语文',score,0)) as '语文',
SUM(IF(`subject`='数学',score,0)) as '数学',
SUM(IF(`subject`='英语',score,0)) as '英语',
SUM(IF(`subject`='政治',score,0)) as '政治'
FROM base_score
GROUP BY userid

温馨提示：

（1）SUM() 是为了能够使用GROUP BY根据userid进行分组，因为每一个userid对应的subject="语文"的记录只有一条，所以SUM() 的值就等于对应那一条记录的score的值。

假如userid =‘001’ and subject=‘语文’ 的记录有两条，则此时SUM() 的值将会是这两条记录的和，同理，使用Max()的值将会是这两条记录里面值最大的一个。但是正常情况下，一个user对应一个subject只有一个分数，因此可以使用SUM()、MAX()、MIN()、AVG()等聚合函数都可以达到行转列的效果。

（2）IF(subject=‘语文’,score,0) 作为条件，即对所有subject='语文’的记录的score字段进行SUM()、MAX()、MIN()、AVG()操作，如果score没有值则默认为0。

使用SUM(IF()) 生成列 + WITH ROLLUP 生成汇总行

-- 使用rollup 生成汇总记录
 SELECT userid,IFNULL(`subject`,'total') AS `subject`,SUM(score) AS score
    FROM base_score
    GROUP BY userid,`subject`
    WITH ROLLUP
    HAVING userid IS NOT NULL

-- 使用sum(if) 实现行记录转列记录 + WITH ROLLUP 生成汇总行
    SELECT IFNULL(userid,'total') AS userid,
SUM(IF(`subject`='语文',score,0)) as '语文',
SUM(IF(`subject`='数学',score,0)) as '数学',
SUM(IF(`subject`='英语',score,0)) as '英语',
SUM(IF(`subject`='政治',score,0)) as '政治',
SUM(IF(`subject`='total',score,0)) AS '总计'
FROM (
    SELECT userid,IFNULL(`subject`,'total') AS `subject`,SUM(score) AS score
    FROM base_score
    GROUP BY userid,`subject`
    WITH ROLLUP
    HAVING userid IS NOT NULL
) as tmp
GROUP BY userid
WITH ROLLUP;

使用SUM(IF()) 生成列 + UNION 生成汇总行,并利用 IFNULL将汇总行标题显示为 Total

-- 利用SUM(IF()) 生成列 + UNION 生成汇总行,并利用 IFNULL将汇总行标题显示为 Total
SELECT userid,
SUM(IF(`subject`='语文',score,0)) AS 语文,
SUM(IF(`subject`='数学',score,0)) AS 数学,
SUM(IF(`subject`='英语',score,0)) AS 英语,
SUM(IF(`subject`='政治',score,0)) AS 政治,
SUM(score) AS TOTAL
FROM base_score
GROUP BY userid
UNION
SELECT 'TOTAL',
SUM(IF(`subject`='语文',score,0)) AS 语文,
SUM(IF(`subject`='数学',score,0)) AS 数学,
SUM(IF(`subject`='英语',score,0)) AS 英语,
SUM(IF(`subject`='政治',score,0)) AS 政治,
SUM(score) FROM base_score

利用SUM(IF()) 生成列，直接生成结果不再利用子查询

-- 利用SUM(IF()) 生成列 + with rollup 汇总列，直接生成结果不再利用子查询
SELECT userid,
SUM(IF(`subject`='语文',score,0)) AS 语文,
SUM(IF(`subject`='数学',score,0)) AS 数学,
SUM(IF(`subject`='英语',score,0)) AS 英语,
SUM(IF(`subject`='政治',score,0)) AS 政治,
SUM(score) AS TOTAL
FROM base_score
GROUP BY userid WITH ROLLUP;

列转行方法总结

环境准备：建表语句 + 初始化数据

CREATE TABLE base_score1(
    id INT(11) NOT NULL auto_increment,
    userid VARCHAR(20) NOT NULL COMMENT '用户id',
    cn_score DOUBLE COMMENT '语文成绩',
    math_score DOUBLE COMMENT '数学成绩',
    en_score DOUBLE COMMENT '英语成绩',
    po_score DOUBLE COMMENT '政治成绩',
    PRIMARY KEY(id)
)ENGINE = INNODB DEFAULT CHARSET = utf8;

INSERT INTO base_score1(userid,cn_score,math_score,en_score,po_score) VALUES ('001',90,92,80,0);
INSERT INTO base_score1(userid,cn_score,math_score,en_score,po_score) VALUES ('002',88,90,75.5,0);
INSERT INTO base_score1(userid,cn_score,math_score,en_score,po_score) VALUES ('003',70,85,90,82);

select * from  base_score1

SELECT userid,'语文' AS course,cn_score AS score FROM base_score1
UNION ALL
SELECT userid,'数学' AS course,math_score AS score FROM base_score1
UNION ALL
SELECT userid,'英语' AS course,en_score AS score FROM base_score1
UNION ALL
SELECT userid,'政治' AS course,po_score AS score FROM base_score1

拓展：UNION与UNION ALL的区别

1. 对重复结果的处理：UNION会去掉重复记录，UNION ALL不会；

2. 对排序的处理：UNION会排序，UNION ALL只是简单地将两个结果集合并；

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3. 效率方面的区别：因为UNION 会做去重和排序处理，因此效率比UNION ALL慢很多；