mysql中如何查询序列号

CREATE TABLE products (
    product_id INT AUTO_INCREMENT PRIMARY KEY,
    product_name VARCHAR(100) NOT NULL
);

INSERT INTO products (product_name) VALUES ('Product A'), ('Product B');

SELECT product_id FROM products;

CREATE TABLE sequence_table (
    seq_name VARCHAR(50) PRIMARY KEY,
    next_val INT NOT NULL
);

INSERT INTO sequence_table (seq_name, next_val) VALUES ('product_seq', 1);

UPDATE sequence_table SET next_val = LAST_INSERT_ID(next_val + 1) WHERE seq_name = 'product_seq';
SELECT LAST_INSERT_ID();

DELIMITER //

CREATE FUNCTION generate_sequence()
RETURNS INT
DETERMINISTIC
BEGIN
    DECLARE current_val INT;
    UPDATE sequence_table SET current_val = LAST_INSERT_ID(current_val + 1) WHERE seq_name = 'product_seq';
    RETURN LAST_INSERT_ID();
END //

DELIMITER ;

SELECT generate_sequence() AS sequence_number;

ALTER TABLE products AUTO_INCREMENT = 1;

START TRANSACTION;
SELECT next_val INTO @next_val FROM sequence_table WHERE seq_name = 'product_seq' FOR UPDATE;
UPDATE sequence_table SET next_val = @next_val + 1 WHERE seq_name = 'product_seq';
COMMIT;