Two different methods of obtaining max row - sql

Question

The first statement is how I have needed to pull a min row based on the org's needs I work for. At first, I would MIN(DATEFIELD) but if someone has two entries on the same day, we had problems. Next I tried MIN(OP__DOCID) where OP__DOCID is the table's unique key. Problem here is if someone ever back-dated an entry they forgot to create, the results would be inaccurate. So, I came up with the below statement. It ensures I get the most recent result from each unique admission.
SELECT OP__DocID
FROM FD__CNSLG_BASIS24 AS PC1
WHERE (OP__DOCID =
(SELECT TOP(1)OP__DocID
FROM FD__CNSLG_BASIS24 AS PC2
WHERE PC2.ClientKey = PC1.Clientkey and PC2.ProgramAdmitKey = PC1.Programadmitkey
ORDER BY Date_Screening
)
)
Recently, I have learned about OVER(PARTITION BY) and have been curious as to the subtle differences in how it works v.s. the statement above, because I do get different result.
SELECT OP__DocID = Min(OP__DOCID) OVER (Partition BY Clientkey, Programadmitkey)
FROM FD__CNSLG_BASIS24
Any insight, or links to other pages I could read would be extremely helpful.
Thanks!

Answer 1

Just use window functions:
select pc.*
from (select pc.*,
row_number() over (partition by Clientkey, ProgramAdmitKey
order by Date_Screening -- do you mean DESC?
) as seqnum
from FD__CNSLG_BASIS24 PC
) pc
where seqnum = 1;
Note: this gets the first record based on the screening date. You might want DESC to get the most recent.

Answer 2

My Solution, for those that were curious
I want to go back and substitute the SELECT TOP(1) for the ROW_Number() function, but I needed to get a report out, and this is providing what I need. Thanks for everyone's help.
SET ANSI_NULLS ON
GO
SET QUOTED_IDENTIFIER ON
GO
BEGIN
SET NOCOUNT ON;
Declare
#StartDate Date,
#EndDate Date
SET #StartDate = '1/1/2016'
SET #EndDate = '6/1/2016'
WITH CNSL_Clients AS (
SELECT PC_CNT.Clientkey, PC_Cnt.ProgramAdmitKey, PC_Cnt.OP__DOCID
FROM FD__Primary_Client as PC_Cnt
INNER JOIN VW__Cnsl_Session_Count_IndvFamOnly as cnt
ON PC_Cnt.Clientkey = CNT.Clientkey AND PC_Cnt.ProgramAdmitKey = CNT.ProgramAdmitKey
WHERE ((pc_CNT.StartDate between #StartDate AND #EndDate) OR (pc_CNT.StartDate <= #StartDate AND pc_CNT.ENDDate >= #StartDate) OR (pc_CNT.StartDate <= #StartDate AND pc_CNT.ENDDate is null))
AND CNT.SessionCount>=6
),
FIRST_BASIS AS (
SELECT CB24_1.OP__DOCID, CB24_1.Date_Screening, CB24_1.ClientKey, CB24_1.ProgramAdmitKey, CB24_1.Composite_score, CB24_1.Depression_Results,CB24_1.Emotional_Results, CB24_1.Relationships_Results
FROM FD__CNSLG_BASIS24 AS CB24_1
WHERE (CB24_1.OP__DOCID =
(Select TOP(1) CB24_2.OP__DOCID
FROM FD__CNSLG_BASIS24 AS CB24_2
Inner JOIN CNSL_Clients
ON CB24_2.ClientKey = CNSL_Clients.ClientKey AND CB24_2.ProgramAdmitKey = CNSL_Clients.ProgramAdmitKey
WHERE (CB24_1.ClientKey = CB24_2.ClientKey) AND (CB24_1.ProgramAdmitKey = CB24_2.ProgramAdmitKey)
ORDER BY CB24_2.Date_Screening))
),
RECENT_BASIS AS (
SELECT CB24_1.OP__DOCID, CB24_1.Date_Screening, CB24_1.ClientKey, CB24_1.ProgramAdmitKey, CB24_1.Composite_score, CB24_1.Depression_Results,CB24_1.Emotional_Results, CB24_1.Relationships_Results
FROM FD__CNSLG_BASIS24 AS CB24_1
WHERE (CB24_1.OP__DOCID =
(Select TOP(1) CB24_2.OP__DOCID
FROM FD__CNSLG_BASIS24 AS CB24_2
Inner JOIN CNSL_Clients
ON CB24_2.ClientKey = CNSL_Clients.ClientKey AND CB24_2.ProgramAdmitKey = CNSL_Clients.ProgramAdmitKey
WHERE (CB24_1.ClientKey = CB24_2.ClientKey) AND (CB24_1.ProgramAdmitKey = CB24_2.ProgramAdmitKey)
ORDER BY CB24_2.Date_Screening DESC))
)
SELECT F.OP__DOCID AS First_DOCID,R.OP__DOCID as Recent_DOCID,F.ClientKey, F.ProgramAdmitKey, F.Composite_Score AS FComposite_Score, R.Composite_Score as RComposite_Score, Composite_Change = R.Composite_Score - F.Composite_Score, F.Depression_Results AS FDepression_Results, R.Depression_Results AS RDepression_Resluts, Depression_Change = R.Depression_Results - F.Depression_Results, F.Emotional_Results AS FEmotional_Resluts, R.Emotional_Results AS REmotionall_Reslu, Emotional_Change = R.Emotional_Results - F.Emotional_Results, F.Relationships_Results AS FRelationships_Resluts, R.Relationships_Results AS RRelationships_Resluts, Relationship_Change = R.Relationships_Results - F.Relationships_Results
FROM First_basis AS F
FULL Outer JOIN RECENT_BASIS AS R
ON F.ClientKey = R.ClientKey AND F.ProgramAdmitKey = R.ProgramAdmitKey
ORDER BY F.ClientKey
END
GO