sql查询：行转列和 列转行

目录

一、行转列

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，直接生成汇总结果，不再利用子查询 

5、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

6、动态查询列值不确定的情况

7、合并字段显示：group_concat()

二、列转行

---

一、行转列

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。

表及数据sql：

1. CREATE TABLE `tb_score` (
2. `id` int(11) NOT NULL AUTO_INCREMENT,
3. `userid` varchar(20) NOT NULL COMMENT '用户id',
4. `subjectName` varchar(20) DEFAULT NULL COMMENT '科目',
5. `score` double DEFAULT NULL COMMENT '成绩',
6. PRIMARY KEY (`id`)
7. ) ENGINE=InnoDB AUTO_INCREMENT=15 DEFAULT CHARSET=utf8;
9. INSERT INTO `tb_score`(`id`, `userid`, `subjectName`, `score`) VALUES (1, '001', '语文', 90);
10. INSERT INTO `tb_score`(`id`, `userid`, `subjectName`, `score`) VALUES (2, '001', '数学', 92);
11. INSERT INTO `tb_score`(`id`, `userid`, `subjectName`, `score`) VALUES (3, '001', '英语', 80);
12. INSERT INTO `tb_score`(`id`, `userid`, `subjectName`, `score`) VALUES (4, '002', '语文', 88);
13. INSERT INTO `tb_score`(`id`, `userid`, `subjectName`, `score`) VALUES (5, '002', '数学', 90);
14. INSERT INTO `tb_score`(`id`, `userid`, `subjectName`, `score`) VALUES (6, '002', '英语', 75.5);
15. INSERT INTO `tb_score`(`id`, `userid`, `subjectName`, `score`) VALUES (7, '003', '语文', 70);
16. INSERT INTO `tb_score`(`id`, `userid`, `subjectName`, `score`) VALUES (8, '003', '数学', 85);
17. INSERT INTO `tb_score`(`id`, `userid`, `subjectName`, `score`) VALUES (9, '003', '英语', 90);
18. INSERT INTO `tb_score`(`id`, `userid`, `subjectName`, `score`) VALUES (10, '003', '政治', 82);
19. INSERT INTO `tb_score`(`id`, `userid`, `subjectName`, `score`) VALUES (11, '004', '政治', 82);
20. INSERT INTO `tb_score`(`id`, `userid`, `subjectName`, `score`) VALUES (12, '004', '英语', 83);

行数据：

列数据：

1、使用case…when…then 

SELECT
userid,
SUM( CASE subjectName WHEN '语文' THEN score ELSE 0 END ) '语文',
SUM( CASE subjectName WHEN '数学' THEN score ELSE 0 END ) '数学',
SUM( CASE subjectName WHEN '英语' THEN score ELSE 0 END ) '英语',
SUM( CASE subjectName WHEN '政治' THEN score ELSE 0 END ) '政治' 
FROM
tb_score 
GROUP BY
userid;

 2、使用SUM(IF()) 生成列 

1. SELECT
2. userid,
3. SUM( IF ( subjectName = '语文', score, 0 ) ) '语文',
4. SUM( IF ( subjectName = '数学', score, 0 ) ) '数学',
5. SUM( IF ( subjectName = '英语', score, 0 ) ) '英语',
6. SUM( IF ( subjectName = '政治', score, 0 ) ) '政治'
7. FROM
8. tb_score
9. GROUP BY
10. userid;

3、使用SUM(IF()) 生成列 + WITH ROLLUP 生成汇总行 

MySQL提供了 group by with rollup 函数进行group by 字段的汇总，但是与order by 互斥的不能同时用。

SELECT
IFNULL( userid, 'total' ) AS userid,
SUM( IF ( subjectName = '语文', score, 0 ) ) '语文',
SUM( IF ( subjectName = '数学', score, 0 ) ) '数学',
SUM( IF ( subjectName = '英语', score, 0 ) ) '英语',
SUM( IF ( subjectName = '政治', score, 0 ) ) '政治',
SUM( IF ( subjectName = 'total', score, 0 ) ) AS 'total' 
FROM
(
SELECT
userid,
IFNULL( subjectName, 'total' ) AS subjectName,
SUM( score ) AS score 
FROM
tb_score 
GROUP BY userid, subjectName WITH ROLLUP 
) AS a
GROUP BY userid
WITH ROLLUP;

4、使用SUM(IF()) 生成列，直接生成汇总结果，不再利用子查询 

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

5、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

SELECT userid,
SUM(IF(subjectName='语文',score,0)) AS '语文',
SUM(IF(subjectName='数学',score,0)) AS '数学',
SUM(IF(subjectName='英语',score,0)) AS '英语',
SUM(IF(subjectName='政治',score,0)) AS '政治',
SUM(score) AS total
FROM tb_score
GROUP BY userid
UNION
SELECT 'total',SUM(IF(subjectName='语文',score,0)) AS '语文',
SUM(IF(subjectName='数学',score,0)) AS '数学',
SUM(IF(subjectName='英语',score,0)) AS '英语',
SUM(IF(subjectName='政治',score,0)) AS '政治',
SUM(score) FROM tb_score;

6、动态查询列值不确定的情况

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 ;
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;
7. PREPARE stmt FROM @QQ;
8. EXECUTE stmt;
9. DEALLOCATE PREPARE stmt;

3、4、5、6、执行结果如下：

7、合并字段显示：group_concat()

SELECT userid,GROUP_CONCAT(`subjectName`,':',score)AS 成绩 FROM tb_score GROUP BY userid;

group_concat() 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 是根据group by指定的列进行分组。

执行结果:

二、列转行

1. CREATE TABLE tb_score1(
2. id INT(11) NOT NULL auto_increment,
3. userid VARCHAR(20) NOT NULL COMMENT '用户id',
4. chinese_score DOUBLE COMMENT '语文成绩',
5. math_score DOUBLE COMMENT '数学成绩',
6. english_score DOUBLE COMMENT '英语成绩',
7. politics_score DOUBLE COMMENT '政治成绩',
8. PRIMARY KEY(id)
9. )ENGINE = INNODB DEFAULT CHARSET = utf8;
11. INSERT INTO tb_score1(userid,chinese_score,math_score,english_score,politics_score) VALUES ('001',90,92,80,0);
12. INSERT INTO tb_score1(userid,chinese_score,math_score,english_score,politics_score) VALUES ('002',88,90,75.5,0);
13. INSERT INTO tb_score1(userid,chinese_score,math_score,english_score,politics_score) VALUES ('003',70,85,90,82);
14. INSERT INTO tb_score1(userid,chinese_score,math_score,english_score,politics_score) VALUES ('003',0,0,83,82);
16. SELECT * FROM tb_score1;

查询结果：

列转行：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。

select userId,'语文' as subjectName,chinese_score as score from tb_score1
union all
select userId,'数学' as subjectName,math_score as score from tb_score1
union all
select userId,'英语' as subjectName,english_score as score from tb_score1
union all
select userId,'政治' as subjectName,politics_score as score from tb_score1;

转换后结果：

UNION ： 会去掉重复记录,会排序,因为UNION 会做去重和排序处理,效率比UNION ALL慢很多。

UNION ALL ：不会对结果进行去重处理，只是简单地将两个结果集合并。

参考文章：

一篇文章搞定mysql的 行转列（7种方法） 和 列转行