ssrsチャートのSQLクエリ式で存在しない値を処理する

上記の回答のように、外部結合とある種のカレンダーテーブルが必要になります。これはテストされていませんが、うまくいくと思います：

with dateCTE as
(
     select cast('2012-01-01' as datetime) dateValue -- start date
     union all
     select DateAdd(mm, 1, dateValue)
     from    dateCTE   
     where   dateValue < '2012-12-30' -- end date
 )
SELECT
MONTH(dateCTE.dateValue) AS 'MONTH',
COUNT(CASE WHEN @Worker_ID1 IS NULL OR @Worker_ID1 = Worker.ID THEN 1 END) AS 'Worker1',
COUNT(CASE WHEN @Worker_ID2 IS NULL OR @Worker_ID2 = Worker.ID THEN 1 END) AS 'Worker2',
COUNT(CASE WHEN @Worker_ID3 IS NULL OR @Worker_ID3 = Worker.ID THEN 1 END) AS 'Worker3',
COUNT(CASE WHEN @Worker_ID4 IS NULL OR @Worker_ID4 = Worker.ID THEN 1 END) AS 'Worker4',
COUNT(CASE WHEN @Worker_ID5 IS NULL OR @Worker_ID5 = Worker.ID THEN 1 END) AS 'Worker5'

FROM dateCTE
LEFT JOIN Ord on MONTH(dateCTE.datevalue) = MONTH(Ord.OrdDate)
JOIN Prod ON Ord.Prod_ID = Prod.ID
JOIN ProdType ON Prod.ProdType_ID = ProdType.ID
JOIN Groupord ON Ord.Groupord_ID = Groupord.ID
JOIN Worker ON Groupord.Worker_ID = Worker.ID

WHERE (@Year = YEAR(Ord.OrdDate) or ORD.prod_id is null)
AND (@DrugType_ID IS NULL OR @ProdType_ID = ProdType.ID)

GROUP BY MONTH(dateCTE.dateValue)
OPTION  (MAXRECURSION 0)