mysql生成sequence

CREATE TABLE users (
    id INT AUTO_INCREMENT PRIMARY KEY,
    name VARCHAR(255) NOT NULL
);

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

DELIMITER $$

CREATE PROCEDURE nextval(IN seq_name VARCHAR(50), OUT val INT)
BEGIN
    DECLARE current_val INT;
    SET current_val = (SELECT IFNULL(MAX(id), 0) FROM sequences WHERE name = seq_name);
    SET val = current_val + 1;
    INSERT INTO sequences (name, id) VALUES (seq_name, val);
END$$

DELIMITER ;

CREATE TABLE sequences (
    name VARCHAR(50) PRIMARY KEY,
    id INT NOT NULL
);

CALL nextval('user_seq', @next_id);
SELECT @next_id;