mysql创建序列怎么创建

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

DELIMITER $$

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

DELIMITER ;

DELIMITER $$

CREATE PROCEDURE generate_id(INOUT new_id INT)
BEGIN
    SET new_id = (SELECT IFNULL(MAX(id), 0) + 1 FROM my_table);
END$$

DELIMITER ;

CREATE TABLE sequence_table (
    seq_name VARCHAR(50) PRIMARY KEY,
    current_val INT DEFAULT 0
);

INSERT INTO sequence_table (seq_name, current_val) VALUES ('my_sequence', 0);

DELIMITER $$

CREATE PROCEDURE next_seq_val(IN seq_name VARCHAR(50), OUT next_val INT)
BEGIN
    UPDATE sequence_table SET current_val = current_val + 1 WHERE seq_name = seq_name;
    SELECT current_val INTO next_val FROM sequence_table WHERE seq_name = seq_name;
END$$

DELIMITER ;