mysql的行转列和列转行

桃扇骨 2022-12-19 06:14 182阅读 0赞

**一、行转列**

即将原本同一列下多行的不同内容作为多个字段，输出对应内容。

建表语句

1.  `DROP TABLE IF EXISTS tb_score;`
2.   
3.  `CREATE TABLE tb_score(`
4.  `id INT(11) NOT NULL auto_increment,`
5.  `userid VARCHAR(20) NOT NULL COMMENT '用户id',`
6.  `subject VARCHAR(20) COMMENT '科目',`
7.  `score DOUBLE COMMENT '成绩',`
8.  `PRIMARY KEY(id)`
9.  `)ENGINE = INNODB DEFAULT CHARSET = utf8;`

插入数据

1.  `INSERT INTO tb_score(userid,subject,score) VALUES ('001','语文',90);`
2.  `INSERT INTO tb_score(userid,subject,score) VALUES ('001','数学',92);`
3.  `INSERT INTO tb_score(userid,subject,score) VALUES ('001','英语',80);`
4.  `INSERT INTO tb_score(userid,subject,score) VALUES ('002','语文',88);`
5.  `INSERT INTO tb_score(userid,subject,score) VALUES ('002','数学',90);`
6.  `INSERT INTO tb_score(userid,subject,score) VALUES ('002','英语',75.5);`
7.  `INSERT INTO tb_score(userid,subject,score) VALUES ('003','语文',70);`
8.  `INSERT INTO tb_score(userid,subject,score) VALUES ('003','数学',85);`
9.  `INSERT INTO tb_score(userid,subject,score) VALUES ('003','英语',90);`
10. `INSERT INTO tb_score(userid,subject,score) VALUES ('003','政治',82);`

查询数据表中的内容（即转换前的结果）

SELECT * FROM tb_score

![mysql 行转列 列转行][mysql _]

先来看一下转换后的结果：

![mysql 行转列 列转行][mysql _ 1]

*可以看出，这里行转列是将原来的subject字段的多行内容选出来，作为结果集中的不同列，并根据userid进行分组显示对应的score。*

**1、使用case...when....then 进行行转列**

1.  `SELECT userid,`
2.  ``SUM(CASE `subject` WHEN '语文' THEN score ELSE 0 END) as '语文',``
3.  ``SUM(CASE `subject` WHEN '数学' THEN score ELSE 0 END) as '数学',``
4.  ``SUM(CASE `subject` WHEN '英语' THEN score ELSE 0 END) as '英语',``
5.  ``SUM(CASE `subject` WHEN '政治' THEN score ELSE 0 END) as '政治'``
6.  `FROM tb_score`
7.  `GROUP BY userid`

**2、使用IF() 进行行转列：**

1.  `SELECT userid,`
2.  ``SUM(IF(`subject`='语文',score,0)) as '语文',``
3.  ``SUM(IF(`subject`='数学',score,0)) as '数学',``
4.  ``SUM(IF(`subject`='英语',score,0)) as '英语',``
5.  ``SUM(IF(`subject`='政治',score,0)) as '政治'``
6.  `FROM tb_score`
7.  `GROUP BY userid`

注意点：

（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。

**3、利用SUM(IF()) 生成列 + WITH ROLLUP 生成汇总行,并利用 IFNULL将汇总行标题显示为Total**

1.  `SELECT IFNULL(userid,'total') AS userid,`
2.  ``SUM(IF(`subject`='语文',score,0)) AS 语文,``
3.  ``SUM(IF(`subject`='数学',score,0)) AS 数学,``
4.  ``SUM(IF(`subject`='英语',score,0)) AS 英语,``
5.  ``SUM(IF(`subject`='政治',score,0)) AS 政治,``
6.  ``SUM(IF(`subject`='total',score,0)) AS total``
7.  `FROM(`
8.  ``SELECT userid,IFNULL(`subject`,'total') AS `subject`,SUM(score) AS score``
9.  `FROM tb_score`
10. ``GROUP BY userid,`subject` ``
11. `WITH ROLLUP`
12. `HAVING userid IS NOT NULL`
13. `)AS A`
14. `GROUP BY userid`
15. `WITH ROLLUP;`

运行结果：

![mysql 行转列 列转行][mysql _ 2]

**4、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**

1.  `SELECT userid,`
2.  ``SUM(IF(`subject`='语文',score,0)) AS 语文,``
3.  ``SUM(IF(`subject`='数学',score,0)) AS 数学,``
4.  ``SUM(IF(`subject`='英语',score,0)) AS 英语,``
5.  ``SUM(IF(`subject`='政治',score,0)) AS 政治,``
6.  `SUM(score) AS TOTAL`
7.  `FROM tb_score`
8.  `GROUP BY userid`
9.  `UNION`
10. ``SELECT 'TOTAL',SUM(IF(`subject`='语文',score,0)) AS 语文,``
11. ``SUM(IF(`subject`='数学',score,0)) AS 数学,``
12. ``SUM(IF(`subject`='英语',score,0)) AS 英语,``
13. ``SUM(IF(`subject`='政治',score,0)) AS 政治,``
14. `SUM(score) FROM tb_score`

运行结果：

![mysql 行转列 列转行][mysql _ 3]

**5、利用SUM(IF()) 生成列，直接生成结果不再利用子查询**

1.  `SELECT IFNULL(userid,'TOTAL') AS userid,`
2.  ``SUM(IF(`subject`='语文',score,0)) AS 语文,``
3.  ``SUM(IF(`subject`='数学',score,0)) AS 数学,``
4.  ``SUM(IF(`subject`='英语',score,0)) AS 英语,``
5.  ``SUM(IF(`subject`='政治',score,0)) AS 政治,``
6.  `SUM(score) AS TOTAL`
7.  `FROM tb_score`
8.  `GROUP BY userid WITH ROLLUP;`

运行结果：

![mysql 行转列 列转行][mysql _ 4]

**6、动态，适用于列不确定情况**

1.  `SET @EE='';`
2.  `select @EE :=CONCAT(@EE,'sum(if(subject= \'',subject,'\',score,0)) as ',subject, ',') AS aa FROM (SELECT DISTINCT subject FROM tb_score) A ;`
3.   
4.  `SET @QQ = CONCAT('select ifnull(userid,\'TOTAL\')as userid,',@EE,' sum(score) as TOTAL from tb_score group by userid WITH ROLLUP');`
5.  `-- SELECT @QQ;`
6.   
7.  `PREPARE stmt FROM @QQ;`
8.  `EXECUTE stmt;`
9.  `DEALLOCATE PREPARE stmt;`

运行结果：

![mysql 行转列 列转行][mysql _ 5]

![mysql 行转列 列转行][mysql _ 6]

**7、合并字段显示：利用group\_concat()**

1.  ``SELECT userid,GROUP_CONCAT(`subject`,":",score)AS 成绩 FROM tb_score``
2.  `GROUP BY userid`

运行结果：

![mysql 行转列 列转行][mysql _ 7]

group\_concat()，手册上说明:该函数返回带有来自一个组的连接的非NULL值的字符串结果。  
比较抽象，难以理解。通俗点理解，其实是这样的：group\_concat()会计算哪些行属于同一组，将属于同一组的列显示出来。要返回哪些列，由函数参数(就是字段名)决定。分组必须有个标准，就是根据group by指定的列进行分组。

*结论：groupconcat()函数可以很好的建属于同一分组的多个行转化为一个列。*

**三、列转行**

建表语句：

1.  `CREATE TABLE tb_score1(`
2.  `id INT(11) NOT NULL auto_increment,`
3.  `userid VARCHAR(20) NOT NULL COMMENT '用户id',`
4.  `cn_score DOUBLE COMMENT '语文成绩',`
5.  `math_score DOUBLE COMMENT '数学成绩',`
6.  `en_score DOUBLE COMMENT '英语成绩',`
7.  `po_score DOUBLE COMMENT '政治成绩',`
8.  `PRIMARY KEY(id)`
9.  `)ENGINE = INNODB DEFAULT CHARSET = utf8;`

插入数据：

1.  `INSERT INTO tb_score1(userid,cn_score,math_score,en_score,po_score) VALUES ('001',90,92,80,0);`
2.  `INSERT INTO tb_score1(userid,cn_score,math_score,en_score,po_score) VALUES ('002',88,90,75.5,0);`
3.  `INSERT INTO tb_score1(userid,cn_score,math_score,en_score,po_score) VALUES ('003',70,85,90,82);`

查询数据表中的内容（即转换前的结果）

SELECT * FROM tb_score1

![mysql 行转列 列转行][mysql _ 8]  
转换后：  
![mysql 行转列 列转行][mysql _ 9]  
*本质是将userid的每个科目分数分散成一条记录显示出来。*

直接上SQL：

1.  `SELECT userid,'语文' AS course,cn_score AS score FROM tb_score1`
2.  `UNION ALL`
3.  `SELECT userid,'数学' AS course,math_score AS score FROM tb_score1`
4.  `UNION ALL`
5.  `SELECT userid,'英语' AS course,en_score AS score FROM tb_score1`
6.  `UNION ALL`
7.  `SELECT userid,'政治' AS course,po_score AS score FROM tb_score1`
8.  `ORDER BY userid`

这里将每个userid对应的多个科目的成绩查出来，通过UNION ALL将结果集加起来，达到上图的效果。

附：UNION与UNION ALL的区别（摘）：

*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；*

*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；*

[mysql _]: /images/20221120/8b8fdfd4ad154444a7a60c60381ef942.png
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