mysql数据库主键怎么用

CREATE TABLE students (
    id INT AUTO_INCREMENT,
    name VARCHAR(100),
    age INT,
    PRIMARY KEY (id)
);

ALTER TABLE students ADD PRIMARY KEY (id);

INSERT INTO students (id, name, age) VALUES (1, 'Alice', 20) ON DUPLICATE KEY UPDATE age = 20;

ALTER TABLE students MODIFY id BIGINT AUTO_INCREMENT;

ALTER TABLE students DROP PRIMARY KEY;

-- 创建表并定义主键
CREATE TABLE students (
    id INT AUTO_INCREMENT,
    name VARCHAR(100),
    age INT,
    PRIMARY KEY (id)
);

-- 插入数据
INSERT INTO students (name, age) VALUES ('Alice', 20);
INSERT INTO students (name, age) VALUES ('Bob', 22);

-- 尝试插入重复的主键值
INSERT INTO students (id, name, age) VALUES (1, 'Charlie', 25) ON DUPLICATE KEY UPDATE age = 25;

-- 更改主键类型为BIGINT
ALTER TABLE students MODIFY id BIGINT AUTO_INCREMENT;

-- 删除主键
ALTER TABLE students DROP PRIMARY KEY;