with 
    CTE_T as
    (
        select COUNT(*) as TotIsStaffTask
        from Table1
        where IsStaffTask = 1
    ),
    
    CTE_D as
    (
        select 
            b.DID,
            COUNT(*) as TotIsStaffTask
        from Table2 as b
        join Table1 as a 
            on a.AID = b.AID and a.IsStaffTask = 1
        group by b.DID
    )
    
select d.DID
from CTE_D as d
join CTE_T as t 
    on t.TotIsStaffTask = d.TotIsStaffTask

SELECT
	AID
FROM
	Table1 t1
LEFT JOIN
	Table2 t2 IN t1.AID = t2.AID
WHERE
	t1.IsStaffTeak = 1
AND
	t2.AID IS NULL

DECLARE @Table1 TABLE(AID INT, IsStaffTask INT)
INSERT INTO @Table1(AID,IsStaffTask)
SELECT 1, 0 UNION ALL
SELECT 2, 1 UNION ALL
SELECT 3, 1 UNION ALL
SELECT 4, 0;

DECLARE @Table2 TABLE(DID INT, AID INT)
INSERT INTO @Table2(DID,AID)
SELECT 14, 1 UNION ALL
SELECT 14, 2 UNION ALL  -- 14 is missing 3
SELECT 15, 1 UNION ALL   -- 15 has all of 2 and 3
SELECT 15, 2 UNION ALL
SELECT 15, 3;

SELECT t2.DID
FROM @Table2 t2
INNER JOIN @Table1 t1 ON t1.AID=t2.AID
                     AND t1.IsStaffTask=1
GROUP BY t2.DID
HAVING COUNT(*) < (SELECT COUNT(*) FROM @Table1 WHERE IsStaffTask=1);

DECLARE @Table1 TABLE(AID INT, IsStaffTask INT)
INSERT INTO @Table1(AID,IsStaffTask)
SELECT 1, 0 UNION ALL
SELECT 2, 1 UNION ALL
SELECT 3, 1 UNION ALL
SELECT 3, 1 UNION ALL
SELECT 3, 1 UNION ALL
SELECT 4, 0;

DECLARE @Table2 TABLE(DID INT, AID INT)
INSERT INTO @Table2(DID,AID)
SELECT 14, 1 UNION ALL
SELECT 14, 2 UNION ALL
SELECT 14, 2 UNION ALL
SELECT 14, 2 UNION ALL
SELECT 15, 1 UNION ALL
SELECT 15, 1 UNION ALL
SELECT 15, 2 UNION ALL
SELECT 15, 2 UNION ALL
SELECT 15, 3;

SELECT t2.DID
FROM @Table2 t2
INNER JOIN @Table1 t1 ON t1.AID=t2.AID
                     AND t1.IsStaffTask=1
GROUP BY t2.DID
HAVING COUNT(DISTINCT t2.AID) < (SELECT COUNT(DISTINCT AID) FROM @Table1 WHERE IsStaffTask=1);