WITH pre_max AS (
SELECT
    MAX(CHECKUP_DATE) AS CK_DATE,
    MIN(H.MEMBER_CODE) AS CODE,
    MIN(LAST_NAME || FIRST_NAME) AS NAME,
    MAX(WEIGHT) AS WEIGHT
FROM
    HEALTH_CHECKUP AS H
JOIN
    MEMBER_MST AS M
ON  
    H.MEMBER_CODE = M.MEMBER_CODE
GROUP BY
    H.MEMBER_CODE
--HAVING
--    CHECKUP_DATE = MAX(CHECKUP_DATE)
),
pre_min AS(
SELECT
    MIN(CHECKUP_DATE) AS CK_DATE,
    MIN(H.MEMBER_CODE) AS CODE,
    MIN(LAST_NAME || FIRST_NAME) AS NAME,
    MAX(WEIGHT) AS WEIGHT
FROM
    HEALTH_CHECKUP AS H
JOIN
    MEMBER_MST AS M
ON  
    H.MEMBER_CODE = M.MEMBER_CODE
GROUP BY
    H.MEMBER_CODE
--HAVING
--    CHECKUP_DATE = MIN(CHECKUP_DATE)
)
SELECT
    pre_max.CK_DATE AS CK_DATE,
    pre_max.CODE AS CODE,
    pre_max.NAME AS NAME,
    pre_max.WEIGHT AS max,
    pre_min.WEIGHT AS min,
    pre_max.WEIGHT - pre_min.WEIGHT AS  CHG_WT
FROM
    pre_max
JOIN
    pre_min
ON
    pre_max.CODE = pre_min.CODE
ORDER BY 1