Sql Server - Query help (group by with having MAX)

Question

HI,

I'm having a huge problem with one query, this is the data that I have in my table:

entityId             groupId              groupDepth
-------------------- -------------------- -----------
NULL                 1090                 0
56                   1090                 1
222                  1090                 1
226                  1090                 1
227                  1090                 1
228                  1090                 1
234                  1090                 1
248                  1090                 2
249                  1090                 2
250                  1090                 2
251                  1090                 2
252                  1090                 1
256                  1090                 1
261                  1090                 1
288                  1090                 1
294                  1090                 1
300                  1090                 1
4691                 1090                 1
4694                 1090                 1
4697                 1090                 1

So what I would like to do, is to obtain the row with the highest groupDepth when given the entityId and groupId. Example results:

input: entityId = 294, groupId = 1090
entityId             groupId              groupDepth
-------------------- -------------------- -----------
294                  1090                 1


input: entityId = 113, groupId = 1090
entityId             groupId              groupDepth
-------------------- -------------------- -----------
NULL                 1090                 0

I was thinking about something like this:

SELECT * FROM [dbo].[EntityGroup] a 
WHERE EXISTS
(
    SELECT   groupId
    FROM     [dbo].[EntityGroup] b
    WHERE    
              (b.entityId is null or b.entityId = 294) AND
              b.groupId = a.groupId
    GROUP BY  b.groupId
    HAVING    a.groupDepth = max(b.groupDepth) and
              a.entityId = b.entityId 
)

Any help will be greatly appreciated!