Removing duplicates rows in left Joining query - sql

Question

SELECT Rec.[Reg_ID]
,Rec.[Reg_No]
,Rec.[Case_ID]
,Det.Deleted AS CaseDeleted
,[Status].[Status]
,Det.[Unit_Submission_Date] AS [Signature]
,TD.TargetDate AS [Target]
,TD.TargetID
FROM [dbo].[Regestrations] Rec
LEFT JOIN [dbo].[Reg_Details] Det ON Rec.Case_ID = Det.CaseID
LEFT JOIN [dbo].[lkpStatus] [Status] ON Rec.Status_ID = [Status].StatusID
LEFT JOIN TargetDate TD ON TD.RecommId = Rec.Reg_ID
WHERE (Det.MissionID = 50 AND [Status].[Status] = 1 AND Rec.Deleted = 0 AND Det.Deleted = 0)
GROUP BY Rec.[Reg_ID],Rec.[Reg_No],Rec.[Case_ID]
,[Status].[Status]
,Det.[Unit_Submission_Date]
,TD.TargetDate
,Det.Deleted
,TD.TargetID
ORDER BY TD.TargetID desc
I have the above query that is supposed to return rows with unique Rec.[Reg_No]. But joined table TargetDate can have duplicate Rec.[Reg_ID] and if thats the case i get duplicate Rec.[Reg_No] rows in my results.
Table TargetDate has a date time column so i want to eliminate the duplicate Rec.[Reg_No] by selecting 1 row with the latest date value from table TargetDate.
How do modify my Join condition or the query where clause to achive the above?

Answer 1

One way is to use a window function such as ROW_NUMBER() that will generate sequential number based on the specified partition. This generated number can then be used to get the latest row.
SELECT Reg_ID, Reg_No, Case_ID, CaseDeleted, [Status], Signature, [Target], TargetID
FROM
(
SELECT Rec.[Reg_ID]
,Rec.[Reg_No]
,Rec.[Case_ID]
,Det.Deleted AS CaseDeleted
,[Status].[Status]
,Det.[Unit_Submission_Date] AS [Signature]
,TD.TargetDate AS [Target]
,TD.TargetID
,RN = ROW_NUMBER() OVER (PARTITION BY Rec.[Reg_No] ORDER BY TD.TargetID DESC)
FROM [BOI].[dbo].[Regestrations] Rec
LEFT JOIN [dbo].[Reg_Details] Det ON Rec.Case_ID = Det.CaseID
LEFT JOIN [dbo].[lkpStatus] [Status] ON Rec.Status_ID = [Status].StatusID
LEFT JOIN TargetDate TD ON TD.RecommId = Rec.Reg_ID
WHERE (Det.MissionID = 50 AND [Status].[Status] = 1 AND Rec.Deleted = 0 AND Det.Deleted = 0)
) subQuery
WHERE RN = 1
ORDER BY TargetID desc

Answer 2

This query can work correctly if you remove TD.TargetDate from GROUP BY clause and compute what you really need in output - MAX(TD.TargetDate)
But preferable way it to avoid GROUP BY clause at all:
...
FROM [BOI].[dbo].[Regestrations] Rec
LEFT JOIN [dbo].[Reg_Details] Det ON Rec.Case_ID = Det.CaseID
LEFT JOIN [dbo].[lkpStatus] [Status] ON Rec.Status_ID = [Status].StatusID
OUTER APPLY(
SELECT TOP 1 td.TargetDate, td.TargetID
FROM TargetDate TD
WHERE TD.RecommId = Rec.Reg_ID
ORDER BY TD.TargetDate DESC
) td
...

Answer 3

You should first find latest TargetDate for each Reg_ID or RecommId. Then you can use your normal join with TargetDate table just this time with matching both the RecommId and TargetDate.
Try this Query:
SELECT Rec.[Reg_ID]
,Rec.[Reg_No]
,Rec.[Case_ID]
,Det.Deleted AS CaseDeleted
,[Status].[Status]
,Det.[Unit_Submission_Date] AS [Signature]
,TD.TargetDate AS [Target]
,TD.TargetID
FROM [BOI].[dbo].[Regestrations] Rec
LEFT JOIN [dbo].[Reg_Details] Det ON Rec.Case_ID = Det.CaseID
LEFT JOIN [dbo].[lkpStatus] [Status] ON Rec.Status_ID = [Status].StatusID
LEFT JOIN (SELECT RecommId, MAX(TargetDate) MaxTargetDate GROUP BY RecommId) TDWithLatestDate ON TDWithLatestDate.RecommId = Rec.Reg_ID
LEFT OUTER JOIN TargetDate ON TD.RecommId = TDWithLatestDate.RecommId AND TD.TargetDate = TDWithLatestDate.MaxTargetDate
WHERE (Det.MissionID = 50
AND [Status].[Status] = 1
AND Rec.Deleted = 0
AND Det.Deleted = 0
)
GROUP BY Rec.[Reg_ID]
,Rec.[Reg_No]
,Rec.[Case_ID]
,[Status].[Status]
,Det.[Unit_Submission_Date]
,TD.TargetDate
,Det.Deleted
,TD.TargetID
ORDER BY TD.TargetID desc
You can improve this query if you want to avoid tie when there more than one record fighting to be latest.