mysql查询序列语句

CREATE TABLE users (
    id INT AUTO_INCREMENT PRIMARY KEY,
    name VARCHAR(50),
    email VARCHAR(50)
);

DELIMITER //

CREATE FUNCTION generate_sequence() RETURNS INT
BEGIN
    DECLARE seq INT;
    SET seq = (SELECT COALESCE(MAX(id), 0) + 1 FROM users);
    RETURN seq;
END //

DELIMITER ;

CREATE PROCEDURE insert_user(IN name VARCHAR(50), IN email VARCHAR(50))
BEGIN
    INSERT INTO users (id, name, email) VALUES (generate_sequence(), name, email);
END //

DELIMITER //

CREATE TRIGGER trg_adjust_auto_increment
AFTER INSERT ON users
FOR EACH ROW
BEGIN
    DECLARE max_id INT;
    SET max_id = (SELECT MAX(id) FROM users);
    IF max_id <> NEW.id THEN
        UPDATE users SET id = NEW.id WHERE id > NEW.id;
    END IF;
END //

DELIMITER ;