Removing duplicated Data in SQL Server 2008 - sql

Question

I have the bellow code which is comparing the String before it to see if they match. The code is working on records that there are only 1 or 2 dupes.
If there is 3 or more then the current code is not working.
What i need to do is Display the old code as the ID of that line. The New Code i need to be the 1st matched item in the list, in the example it will be 131133. This needs to be the new code for all of the items that match.
I then need the code which has been replaced to appear in the Deleted code and only the code that has been replaced. in the example this should be 141439.
Can i achieve this with my code bellow or do i need to tackle it from another angle?
Thank you in advance.
;WITH MyCTE AS
(
SELECT *,
ROW_NUMBER()OVER (ORDER BY SortField) AS rn
FROM Aron_Reporting.dbo.Customer_Sort
)
SELECT T1.Forename as Forename, T1.pcode, T1.Surname as Surname,T1.SortField AS T1String,
T2.SortField AS T2String,
T1.IDNO as OldCode,
CASE
WHEN T1.SortField IS NULL OR T1.SortField = ' ' OR T2.SortField = ' ' or T2.SortField IS NULL THEN T1.IDNO
WHEN T1.SortField = T2.SortField THEN T2.IDNO ELSE T1.IDNO END AS NewCode,
CASE
WHEN T1.SortField IS NULL OR T1.SortField = ' ' or T2.SortField = ' ' or T2.SortField IS NULL THEN ' '
WHEN T1.SortField = T2.SortField THEN T2.IDNO ELSE ' ' END AS DeleteCode
FROM MyCTE T1
LEFT JOIN MyCTE T2
ON T1.rn = T2.rn+1

Answer 1

I'm not exactly sure what you are trying to do, so hopefully this helps.
Using a sub-query to calculate the desired code can handle any number of duplicates. The sub-query needs to return the first record that is a match (including itself).
The below example is broken up into small steps so you can see exactly how the data is being manipulated.
-- Generate table structure
DECLARE #TestData TABLE (
ID INT
, ValueToCompare VARCHAR(MAX)
, Code INT
, NewCode INT
)
-- Generate test data
INSERT INTO #TestData
( ID, ValueToCompare, Code )
VALUES (1, 'John', 1134), (2, 'Joe', 1546), (3, 'Joe', 1893), (4, 'Joe', 9785), (5, 'Joe', 9452)
-- View the original data
SELECT *
FROM #TestData
-- View what the NewCode will be
SELECT ID
, ValueToCompare
, Code
, (SELECT MIN(Code) -- This subquery uses the MIN statement to grab the first record from a list of matching records
FROM #TestData SubQueryData
WHERE MainQueryData.ValueToCompare = SubQueryData.ValueToCompare
) AS 'New_Code'
FROM #TestData MainQueryData
-- Set the NewCode value
UPDATE #TestData
SET NewCode = (SELECT MIN(Code)
FROM #TestData SubQueryData
WHERE MainQueryData.ValueToCompare = SubQueryData.ValueToCompare
)
FROM #TestData MainQueryData
-- Delete duplicate records
DELETE
FROM #TestData
WHERE Code <> NewCode
-- View the resulting data
SELECT *
FROM #TestData