mysql数据库如何创建序列号

CREATE TABLE users (
    id INT AUTO_INCREMENT PRIMARY KEY,
    name VARCHAR(100) NOT NULL
);

INSERT INTO users (name) VALUES ('Alice');
INSERT INTO users (name) VALUES ('Bob');

SELECT * FROM users;

DELIMITER $$

CREATE TRIGGER generate_id_before_insert
BEFORE INSERT ON users
FOR EACH ROW
BEGIN
    SET NEW.id = (SELECT IFNULL(MAX(id), 0) + 1 FROM users);
END$$

DELIMITER ;

INSERT INTO users (name) VALUES ('Charlie');
INSERT INTO users (name) VALUES ('David');

SELECT * FROM users;

DELIMITER $$

CREATE PROCEDURE generate_id(IN p_name VARCHAR(100), OUT p_id INT)
BEGIN
    SET p_id = (SELECT IFNULL(MAX(id), 0) + 1 FROM users);
    INSERT INTO users (id, name) VALUES (p_id, p_name);
END$$

DELIMITER ;

CALL generate_id('Eve', @user_id);
SELECT @user_id;