学校管理系统的MySQL表结构设计：主键和索引的使用建议

CREATE TABLE students (
    id INT AUTO_INCREMENT PRIMARY KEY,
    name VARCHAR(50),
    age INT,
    gender VARCHAR(10)
);

CREATE TABLE teachers (
    id INT PRIMARY KEY,
    name VARCHAR(50),
    age INT,
    department VARCHAR(50)
);

CREATE TABLE students (
    id INT AUTO_INCREMENT PRIMARY KEY,
    name VARCHAR(50) INDEX,
    age INT,
    gender VARCHAR(10)
);

CREATE TABLE courses (
    id INT AUTO_INCREMENT PRIMARY KEY,
    name VARCHAR(50),
    teacher_id INT,
    start_date DATE,
    INDEX idx_teacher_id (teacher_id),
    INDEX idx_start_date (start_date)
);

CREATE TABLE classes (
    id INT AUTO_INCREMENT PRIMARY KEY,
    name VARCHAR(50),
    teacher_id INT,
    start_date DATE,
    INDEX idx_teacher_start (teacher_id, start_date)
);