如何在mysql中创建序列号

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

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

DELIMITER //
CREATE PROCEDURE getNextSequence()
BEGIN
    DECLARE next_id INT;
    UPDATE sequence_table SET current_value = current_value + 1 WHERE seq_name = 'user_seq';
    SELECT current_value INTO next_id FROM sequence_table WHERE seq_name = 'user_seq';
    SELECT next_id;
END;
//
DELIMITER ;