MySQL行列转换常见的操作方法详解

CREATE TABLE student_scores (
    student_id INT,
    student_name VARCHAR(50),
    subject VARCHAR(50),
    score INT
);

INSERT INTO student_scores VALUES
(1, '张三', '数学', 90),
(1, '张三', '语文', 85),
(1, '张三', '英语', 92),
(2, '李四', '数学', 88),
(2, '李四', '语文', 90),
(2, '李四', '英语', 87),
(3, '王五', '数学', 95),
(3, '王五', '语文', 78),
(3, '王五', '英语', 85);

SELECT 
    student_id,
    student_name,
    MAX(CASE WHEN subject = '数学' THEN score ELSE NULL END) AS '数学',
    MAX(CASE WHEN subject = '语文' THEN score ELSE NULL END) AS '语文',
    MAX(CASE WHEN subject = '英语' THEN score ELSE NULL END) AS '英语'
FROM student_scores
GROUP BY student_id, student_name;

+------------+--------------+--------+--------+--------+
| student_id | student_name | 数学   | 语文   | 英语   |
+------------+--------------+--------+--------+--------+
|          1 | 张三         |     90 |     85 |     92 |
|          2 | 李四         |     88 |     90 |     87 |
|          3 | 王五         |     95 |     78 |     85 |
+------------+--------------+--------+--------+--------+

CREATE TABLE sales_data (
    id INT,
    product_name VARCHAR(50),
    q1_sales INT,
    q2_sales INT,
    q3_sales INT,
    q4_sales INT
);

INSERT INTO sales_data VALUES
(1, '产品A', 120, 150, 180, 200),
(2, '产品B', 90, 110, 130, 150),
(3, '产品C', 200, 220, 240, 260);

SELECT 
    id,
    product_name,
    'Q1' AS quarter,
    q1_sales AS sales
FROM sales_data
UNION ALL
SELECT 
    id,
    product_name,
    'Q2' AS quarter,
    q2_sales AS sales
FROM sales_data
UNION ALL
SELECT 
    id,
    product_name,
    'Q3' AS quarter,
    q3_sales AS sales
FROM sales_data
UNION ALL
SELECT 
    id,
    product_name,
    'Q4' AS quarter,
    q4_sales AS sales
FROM sales_data
ORDER BY id, quarter;

+----+--------------+---------+-------+
| id | product_name | quarter | sales |
+----+--------------+---------+-------+
|  1 | 产品A        | Q1      |   120 |
|  1 | 产品A        | Q2      |   150 |
|  1 | 产品A        | Q3      |   180 |
|  1 | 产品A        | Q4      |   200 |
|  2 | 产品B        | Q1      |    90 |
|  2 | 产品B        | Q2      |   110 |
|  2 | 产品B        | Q3      |   130 |
|  2 | 产品B        | Q4      |   150 |
|  3 | 产品C        | Q1      |   200 |
|  3 | 产品C        | Q2      |   220 |
|  3 | 产品C        | Q3      |   240 |
|  3 | 产品C        | Q4      |   260 |
+----+--------------+---------+-------+

-- 创建存储过程实现动态行转列
DELIMITER //
CREATE PROCEDURE dynamic_pivot()
BEGIN
    DECLARE done INT DEFAULT FALSE;
    DECLARE col_name VARCHAR(50);
    DECLARE col_list TEXT DEFAULT '';
    DECLARE cur CURSOR FOR 
        SELECT DISTINCT subject FROM student_scores;
    DECLARE CONTINUE HANDLER FOR NOT FOUND SET done = TRUE;
    
    OPEN cur;
    read_loop: LOOP
        FETCH cur INTO col_name;
        IF done THEN
            LEAVE read_loop;
        END IF;
        SET col_list = CONCAT(col_list, 
                             IF(col_list = '', '', ', '), 
                             'MAX(CASE WHEN subject = ''', col_name, ''' THEN score ELSE NULL END) AS ''', col_name, '''');
    END LOOP;
    CLOSE cur;
    
    SET @sql = CONCAT('SELECT student_id, student_name, ', col_list, ' FROM student_scores GROUP BY student_id, student_name');
    
    PREPARE stmt FROM @sql;
    EXECUTE stmt;
    DEALLOCATE PREPARE stmt;
END //
DELIMITER ;

-- 调用存储过程
CALL dynamic_pivot();