mysql的游标for循环嵌套

DELIMITER //

CREATE PROCEDURE process_data()
BEGIN
    DECLARE done INT DEFAULT FALSE;
    DECLARE v_id INT;
    DECLARE v_name VARCHAR(255);
    DECLARE cur CURSOR FOR SELECT id, name FROM users;
    DECLARE CONTINUE HANDLER FOR NOT FOUND SET done = TRUE;

    OPEN cur;

    read_loop: LOOP
        FETCH cur INTO v_id, v_name;
        IF done THEN
            LEAVE read_loop;
        END IF;

        -- 嵌套循环示例
        DECLARE nested_done INT DEFAULT FALSE;
        DECLARE v_age INT;
        DECLARE nested_cur CURSOR FOR SELECT age FROM user_details WHERE user_id = v_id;
        DECLARE CONTINUE HANDLER FOR NOT FOUND SET nested_done = TRUE;

        OPEN nested_cur;

        nested_read_loop: LOOP
            FETCH nested_cur INTO v_age;
            IF nested_done THEN
                LEAVE nested_read_loop;
            END IF;

            -- 处理嵌套循环中的数据
            SELECT CONCAT('User ID: ', v_id, ', Name: ', v_name, ', Age: ', v_age) AS result;
        END LOOP;

        CLOSE nested_cur;
    END LOOP;

    CLOSE cur;
END //

DELIMITER ;

CALL process_data();