MySQL实现列转行与行转列的操作代码

CREATE TABLE scores (
    name VARCHAR(50),
    subject VARCHAR(20),
    score INT
);

INSERT INTO scores (name, subject, score) VALUES
('Alice', 'Math', 95),
('Alice', 'English', 88),
('Bob', 'Math', 76),
('Bob', 'English', 92);

SELECT * FROM scores;
+-------+---------+-------+
| name  | subject | score |
+-------+---------+-------+
| Alice | Math    |    95 |
| Alice | English |    88 |
| Bob   | Math    |    76 |
| Bob   | English |    92 |
+-------+---------+-------+

SELECT
    name,
    MAX(CASE WHEN subject = 'Math' THEN score ELSE NULL END) AS Math,
    MAX(CASE WHEN subject = 'English' THEN score ELSE NULL END) AS English
FROM
    scores
GROUP BY
    name;

+-------+------+---------+
| name  | Math | English |
+-------+------+---------+
| Alice |   95 |      88 |
| Bob   |   76 |      92 |
+-------+------+---------+

CREATE TABLE students (
    name VARCHAR(50),
    Math INT,
    English INT
);

INSERT INTO students (name, Math, English) VALUES
('Alice', 95, 88),
('Bob', 76, 92);

SELECT * FROM students;
+-------+------+---------+
| name  | Math | English |
+-------+------+---------+
| Alice |   95 |      88 |
| Bob   |   76 |      92 |
+-------+------+---------+

SELECT
    name,
    'Math' AS subject,
    Math AS score
FROM
    students
UNION ALL
SELECT
    name,
    'English' AS subject,
    English AS score
FROM
    students;

+-------+---------+-------+
| name  | subject | score |
+-------+---------+-------+
| Alice | Math    |    95 |
| Bob   | Math    |    76 |
| Alice | English |    88 |
| Bob   | English |    92 |
+-------+---------+-------+