Select MAX() or Select TOP 1 on Join - sql

Question

I'm working with the following code to only get one associated person per case, using the MAX Associated Type to get the top 1.
Associated Type is not a GUID, rather looks like:
Responsible Party, Primary Physician, etc.
It just so happens that Responsible Party is the last alphabetical option, so it's a lucky workaround. Not every case has a responsible party, however, and if there isn't a responsible party, the next top associated person is 'good enough' and will be highlighted as a data error anyway.
The result shows every single associated person (rather than top 1), but shows all of them as Responsible Party, which is not true. What am I doing wrong here?
FROM T_LatestIFSP Ltst
LEFT OUTER JOIN (
SELECT
Clas.ClientCase_ID,
MAX(Astp.AssociatedType) AS AssociatedType
FROM
T_ClientAssociatedPerson Clas
Inner Join T_AssociatedType Astp
ON Clas.AssociatedType_ID = Astp.AssociatedType_ID
GROUP BY Clas.ClientCase_ID
) AS Astp ON Ltst.ClientCase_ID = Astp.ClientCase_ID
LEFT OUTER JOIN T_ClientAssociatedPerson Clas
on Clas.ClientCase_ID = Astp.ClientCase_ID
LEFT OUTER JOIN T_AssociatedPerson Aspr
ON Aspr.AssociatedPerson_ID = Clas.AssociatedPerson_ID

Answer 1

To get AssocId in the select, you have to do a self join.
LEFT OUTER JOIN
(your subselect with max(AssociatedType) in it) AS Astp
INNER JOIN T_AssociatedType AS Astp2
ON (whatever the primary key is on that table)
Then you can add astp2.AssociationTypeId to the original SELECT.

Answer 2

You can try this query.
Make rn from your order condition in CASE WHEN
You can use Rank with window function to make rank number in subquery, then get rnk=1 data row.
;WITH CTE AS (
SELECT ClientCase_ID,
AssociatedPerson_ID,
AssociatedPersonType,
AssociatedType_ID,
RANK() OVER(PARTITION BY ClientCase_ID ORDER BY rn desc,AssociatedPerson_ID) rnk
FROM (
SELECT t1.ClientCase_ID,
t1.AssociatedPerson_ID,
t1.AssociatedPersonType,
t1.AssociatedType_ID,
(CASE
WHEN t1.AssociatedPersonType = 'ResPonsible Party' then 16
WHEN t1.AssociatedPersonType = 'Primary Physician' then 15
ELSE 14
END) rn
FROM T t1
INNER JOIN T t2 ON t1.ClientCase_ID = t2.AssociatedPerson_ID
UNION ALL
SELECT t2.AssociatedPerson_ID,
t1.AssociatedPerson_ID,
t1.AssociatedPersonType,
t2.AssociatedType_ID,
(CASE
WHEN t2.AssociatedPersonType = 'ResPonsible Party' then 16
WHEN t2.AssociatedPersonType = 'Primary Physician' then 15
ELSE 14
END) rn
FROM T t1
INNER JOIN T t2 ON t1.ClientCase_ID = t2.AssociatedPerson_ID
) t1
)
select DISTINCT ClientCase_ID,AssociatedPerson_ID,AssociatedPersonType,AssociatedType_ID
FROM CTE
WHERE rnk = 1
sqlfiddle
Also, you can try to use CROSS APPLY with value instead of UNION ALL
;with CTE AS (
SELECT v.*, (CASE
WHEN v.AssociatedPersonType = 'ResPonsible Party' then 16
WHEN v.AssociatedPersonType = 'Primary Physician' then 15
ELSE 14
END) rn
FROM T t1
INNER JOIN T t2 ON t1.ClientCase_ID = t2.AssociatedPerson_ID
CROSS APPLY (VALUES
(t1.ClientCase_ID,t1.AssociatedPerson_ID,t1.AssociatedPersonType, t1.AssociatedType_ID),
(t2.AssociatedPerson_ID,t1.AssociatedPerson_ID,t2.AssociatedPersonType, t2.AssociatedType_ID)
) v (ClientCase_ID,AssociatedPerson_ID,AssociatedPersonType,AssociatedType_ID)
)
SELECT distinct ClientCase_ID,AssociatedPerson_ID,AssociatedPersonType,AssociatedType_ID
FROM
(
SELECT *,
RANK() OVER(PARTITION BY ClientCase_ID ORDER BY rn desc,AssociatedPerson_ID) rnk
FROM CTE
) t1
WHERE rnk = 1
sqlfiddle
Note
you can add your customer order number in CASE WHEN
[Results]:
| ClientCase_ID | AssociatedPerson_ID | AssociatedPersonType | AssociatedType_ID |
|---------------|---------------------|----------------------|-------------------|
| 01 | 01 | ResPonsible Party | 16 |
| 02 | 03 | Physician Therapist | 24 |

Answer 3

I solved the problem with the following code:
LEFT OUTER JOIN T_ClientAssociatedPerson Clas
on Clas.ClientCase_ID = Ltst.ClientCase_ID
and
CASE
WHEN Clas.AssociatedType_ID = 16 AND Clas.ClientCase_ID = Ltst.ClientCase_ID THEN 1
WHEN Clas.AssociatedType_ID <> 16 AND Clas.AssociatedType_ID = (
SELECT TOP 1 Clas.AssociatedType_ID
FROM T_ClientAssociatedPerson Clas
WHERE Clas.ClientCase_ID = Ltst.ClientCase_ID
ORDER BY AssociatedType_ID DESC
) THEN 1
ELSE 0
END = 1