SELECT site,
       ItemGroup,
       MONTH,
       year,
       SUM(ISNULL(value, 0)) value
FROM
(
    SELECT site,
           CASE
               WHEN whse = (IIF(SITE = 'PVD', 'BTL', 'BTLT'))
                    AND PRODUCT_CODE = 'PFG' THEN
                   'ItemPC'
               WHEN whse = 'MAIN'
                    AND PRODUCT_CODE LIKE 'NVL%' THEN
                   'NVL'
               WHEN whse = 'CKH'
                    AND PRODUCT_CODE = 'CKH' THEN
                   'BTP'
               WHEN whse = 'khgb'
                    AND PRODUCT_CODE = 'pfg' THEN
                   'ItemKHGB1571'
           END ItemGroup,
           MONTH,
           year,
           SUM(ISNULL(valueend, 0)) value
    FROM fact_countvalueexist
    GROUP BY MONTH,
             year,
             SITE,
             whse,
             PRODUCT_CODE
) A
WHERE ItemGroup IS NOT NULL
GROUP BY site,
         ItemGroup,
         MONTH,
         year;