Как подсчитать отдельное значение с помощью свертки?

Вот 3 разных варианта. У меня нет SQL 2000 для проверки, но это должно работать. Каждый вариант может работать по-разному, в зависимости от размера таблицы и структуры данных.

ПРИМЕЧАНИЕ. Для всех, кто видит этот ответ, если вы используете SQL Server 2008 R2 или более позднюю версию, COUNT DISTINCT работает даже при использовании ROLLUP. Это может работать с SQL 2005, но у меня нет экземпляра SQL 05 для тестирования.

Использование подзапроса:

SELECT t.annee, t.mois, t.siteId, t.id, t.cnt, t.downtime
    , (
        SELECT count(distinct i2.department) 
        FROM incident i2 
        WHERE (i2.annee = t.annee 
                    or i2.annee is null and t.annee is null and t.isgroup_annee = 0 
                    or t.isgroup_annee = 1)
            and (i2.mois = t.mois 
                    or i2.mois is null and t.mois is null and t.isgroup_mois = 0 
                    or t.isgroup_mois = 1)
            and (i2.siteId = t.siteId 
                    or i2.siteId is null and t.siteId is null and t.isgroup_siteId = 0  
                    or t.isgroup_siteId = 1)
            and (i2.id = t.id 
                    OR i2.id is null and t.id is null and t.isgroup_id = 0 
                    OR t.isgroup_id = 1)
        ) as departmentCnt
FROM (
    SELECT i.annee, i.mois, i.siteId, i.id, count(i.id) as cnt, sum(i.downtime) as downtime 
        , grouping(i.annee) AS isgroup_annee
        , grouping(i.mois) AS isgroup_mois
        , grouping(i.siteId) AS isgroup_siteId
        , grouping(i.id) AS isgroup_Id
    FROM incident i
    GROUP BY i.annee, i.mois, i.siteId, i.id
    WITH ROLLUP
) t
;

Использование соединения:

SELECT t.annee, t.mois, t.siteId, t.cnt, t.downtime
    , count(distinct i2.department) as departmentCnt
FROM (
    SELECT i.annee, i.mois, i.siteId, i.id, count(i.id) as cnt, sum(i.downtime) as downtime 
        , grouping(i.annee) AS isgroup_annee
        , grouping(i.mois) AS isgroup_mois
        , grouping(i.siteId) AS isgroup_siteId
        , grouping(i.id) AS isgroup_Id
    FROM incident i
    GROUP BY i.annee, i.mois, i.siteId, i.id
    WITH ROLLUP
) t
LEFT JOIN incident i2 
    ON (i2.annee = t.annee 
            or i2.annee is null and t.annee is null and t.isgroup_annee = 0 
            or t.isgroup_annee = 1)
    and (i2.mois = t.mois 
            or i2.mois is null and t.mois is null and t.isgroup_mois = 0 
            or t.isgroup_mois = 1)
    and (i2.siteId = t.siteId 
            or i2.siteId is null and t.siteId is null and t.isgroup_siteId = 0  
            or t.isgroup_siteId = 1)
    and (i2.id = t.id 
            OR i2.id is null and t.id is null and t.isgroup_id = 0 
            OR t.isgroup_id = 1)
GROUP BY t.annee, t.mois, t.siteId, t.id, t.cnt, t.downtime, t.isgroup_annee, t.isgroup_mois, t.isgroup_siteId, t.isgroup_Id
;

используя UNIONs для выполнения ROLLUP вручную:

SELECT i.annee, i.mois, i.siteId, i.id, count(i.id) as cnt, sum(i.downtime) as downtime, count(distinct i.department) as departmentCnt
FROM incident i
GROUP BY i.annee, i.mois, i.siteId, i.id
UNION ALL
SELECT i.annee, i.mois, i.siteId, null as id, count(i.id) as cnt, sum(i.downtime) as downtime, count(distinct i.department) as departmentCnt
FROM incident i
GROUP BY i.annee, i.mois, i.siteId
UNION ALL
SELECT i.annee, i.mois, null as siteId, null as id, count(i.id) as cnt, sum(i.downtime) as downtime, count(distinct i.department) as departmentCnt
FROM incident i
GROUP BY i.annee, i.mois
UNION ALL
SELECT i.annee, null as mois, null as siteId, null as id, count(i.id) as cnt, sum(i.downtime) as downtime, count(distinct i.department) as departmentCnt
FROM incident i
GROUP BY i.annee
UNION ALL
SELECT null as annee, null as mois, null as siteId, null as id, count(i.id) as cnt, sum(i.downtime) as downtime, count(distinct i.department) as departmentCnt
FROM incident i
;