MySQL行列转化方式
作者：袅沫
文章介绍了如何将行数据转化为列数据,并展示了如何使用UNION和UNION ALL的区别,作者分享了个人经验,希望能对大家有所帮助
初始化表结构
CREATE TABLE `student_scores` ( `student_id` int NOT NULL, `student_name` varchar(50) DEFAULT NULL, `math_score` int DEFAULT NULL, `english_score` int DEFAULT NULL, `science_score` int DEFAULT NULL, PRIMARY KEY (`student_id`) ) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_0900_ai_ci; INSERT INTO student_scores (student_id, student_name, math_score, english_score, science_score) VALUES (1, 'Alice', 85, 90, 78), (2, 'Bob', 76, 88, 92), (3, 'Charlie', 90, 85, 80);
查询表数据：
行转化为列
由于不是我们想要的格式，我们将其转化为列式结构：
-- 行数转化为列 SELECT student_id, student_name, 'Math' AS subject, math_score AS score FROM student_scores UNION ALL SELECT student_id, student_name, 'English' AS subject, english_score AS score FROM student_scores UNION ALL SELECT student_id, student_name, 'Science' AS subject, science_score AS score FROM student_scores;
执行结果：
列转化为行
将其作为一张临时表，对其进行行列转化：
select student_id,student_name,
MIN(Case when subject = 'Math' then score end ) as math_score,
MIN(case when subject = 'English' then score end )as english_score,
MIN(case when subject = 'Science' then score end )as science_score
from (
SELECT student_id, student_name, 'Math' AS subject, math_score AS score FROM student_scores
UNION ALL
SELECT student_id, student_name, 'English' AS subject, english_score AS score FROM student_scores
UNION ALL
SELECT student_id, student_name, 'Science' AS subject, science_score AS score FROM student_scores
) AS unpivoted
GROUP BY unpivoted.student_id,unpivoted.student_name
执行结果：
扩展
union 与 union all区别
- UNION：会自动去除合并结果集中的重复记录，只返回唯一的记录。
- UNION ALL：会返回所有记录，包括重复的记录。
总结
以上为个人经验，希望能给大家一个参考，也希望大家多多支持脚本之家。