当我的mysql存储过程没有找到任何结果时，我想抛出一个异常

DECLARE custom_exception CONDITION FOR SQLSTATE '45000';

DECLARE EXIT HANDLER FOR NOT FOUND
BEGIN
    SIGNAL custom_exception
        SET MESSAGE_TEXT = 'No results found';
END;

DELIMITER //

CREATE PROCEDURE my_procedure()
BEGIN
    -- 声明异常变量
    DECLARE custom_exception CONDITION FOR SQLSTATE '45000';

    -- 定义异常处理器
    DECLARE EXIT HANDLER FOR NOT FOUND
    BEGIN
        SIGNAL custom_exception
            SET MESSAGE_TEXT = 'No results found';
    END;

    -- 执行查询语句
    SELECT * FROM your_table WHERE your_condition;
END//

DELIMITER ;