单表：

CREATE TABLE students (
    id INT PRIMARY KEY,
    name VARCHAR(50),
    age INT,
    score FLOAT
);

插入数据：

INSERT INTO students (id, name, age, score) VALUES
(1, '张三', 18, 90.5),
(2, '李四', 19, 85.0),
(3, '王五', 20, 78.5),
(4, '赵六', 21, 92.0);

查询所有数据：

SELECT * FROM students;

多表：

CREATE TABLE scores (
    id INT PRIMARY KEY,
    student_id INT,
    subject VARCHAR(50),
    score FLOAT,
    FOREIGN KEY (student_id) REFERENCES students(id)
);

插入数据：

INSERT INTO scores (id, student_id, subject, score) VALUES
(1, 1, '语文', 85.0),
(2, 1, '数学', 90.5),
(3, 2, '语文', 80.0),
(4, 2, '数学', 88.0),
(5, 3, '语文', 78.5),
(6, 3, '数学', 92.0),
(7, 4, '语文', 90.5),
(8, 4, '数学', 85.0),
(9, 5, '语文', 82.0),
(10, 5, '数学', 89.5);

查询所有数据：

SELECT * FROM scores;

分类汇总排序查：

SELECT subject, COUNT(*) AS count, AVG(score) AS average_score FROM scores GROUP BY subject ORDER BY average_score DESC;