Delete duplicated row and update the row using the duplicated row id - sql-server

Question

This is the Scenario : I have a duplicate rows in my table with the same Id , Name and so on .
1) I have to find the duplicate row matching all the criteria ( this is done)
2) Delete them only if the criteria match
3) Use the id of the deleted record and update the existing row in the table
For this i have created a 2 temp table. Temp1 is the table with all the record. Temp2 consist of duplicated row.
IF OBJECT_ID('tempdb..#Temp1') IS NOT NULL
DROP TABLE #Temp1
IF OBJECT_ID('tempdb..#Temp2') IS NOT NULL
DROP TABLE #Temp2
IF OBJECT_ID('tempdb..#Temp3') IS NOT NULL
DROP TABLE #Temp3
CREATE Table #Temp1 (
Id int,
Name NVARCHAR(64),
StudentNo INT NULL,
ClassCode NVARCHAR(8) NULL,
Section NVARCHAR(8) NULL,
)
INSERT INTO #Temp1 (Id, Name,StudentNo,ClassCode,Section) Values(1,'Joe',123,'A1', 'I')
INSERT INTO #Temp1 (Id, Name,StudentNo,ClassCode,Section) Values(1,'Joe',123,'A1', 'I')
INSERT INTO #Temp1 (Id, Name,StudentNo,ClassCode,Section) Values(2,'Harry',113,'X2', 'H')
INSERT INTO #Temp1 (Id, Name,StudentNo,ClassCode,Section) Values(2,'Harry',113,'X2', 'H')
INSERT INTO #Temp1 (Id, Name,StudentNo,ClassCode,Section) Values(3,'Elle',121,'J1', 'E1')
INSERT INTO #Temp1 (Id, Name,StudentNo,ClassCode,Section) Values(3,'Elle',121,'J1', 'E')
INSERT INTO #Temp1 (Id, Name,StudentNo,ClassCode,Section) Values(8,'Jane',191,'A1', 'E')
INSERT INTO #Temp1 (Id, Name,StudentNo,ClassCode,Section) Values(5,'Silva',811,'S1', 'SE')
INSERT INTO #Temp1 (Id, Name,StudentNo,ClassCode,Section) Values(6,'Juan',411,'S2', 'SE')
INSERT INTO #Temp1 (Id, Name,StudentNo,ClassCode,Section) Values(7,'Carla',431,'S2', 'SE')
;WITH CTE AS (
select
ROW_NUMBER() over (partition by Id
, StudentNo
order by Id, StudentNo)as Duplicate_RowNumber
, * from #Temp1 )
select t1.Id,t1.Name,t1.StudentNo,t1.Section,t1.ClassCode
INTO #Temp2
from CTE as c INNER JOIN #Temp1 as t1 ON t1.Id = c.Id
and t1.StudentNo = t1.StudentNo
and c.Duplicate_RowNumber >1
-- this will have 6 rows all the duplicates are included
--select * from #Temp2
-- this is for output clause
DECLARE #inserted Table (Id int,
Name NVARCHAR(64),
StudentNo INT NULL,
ClassCode NVARCHAR(8) NULL,
Section NVARCHAR(8) NULL)
DELETE FROM #temp1
OUTPUT deleted.Id , deleted.Name ,deleted.StudentNo ,deleted.ClassCode ,deleted.Section into #inserted
WHERE EXISTS ( SELECT * FROM #Temp2 as t2
where #temp1.Id = t2.Id
and #temp1.Name = t2.Name
and #temp1.StudentNo = t2.StudentNo
and #temp1.ClassCode = t2.ClassCode
and #temp1.Section = t2.Section)
-- this is to check what is delete so that i can join it and update the table temp1
select * from #inserted
You can see below the query should not delete the last two highlighted column because the Section does not match. It should only delete matching criteria from Temp1 and Temp2.
Scenario 2 : Delete the duplicate record in Temp1 and use the key in order to update the data to NULL for Section and Classcode . This is what i expect with the highlighted to be NULLs .
You can run this query yourself - just copy and paste.

Answer 1

Yes, for scenario #1 it is going to delete the rows because the problem is in this section.
I added this table for references.
Added this #temp2 table to clarify for later use.
CREATE Table #Temp2 (
Id int,
Name Varchar(64),
StudentNo INT NULL,
ClassCode Varchar(8) NULL,
Section Varchar(8) NULL,
)
IF OBJECT_ID('tempdb..#tmp4') IS NOT NULL
DROP TABLE #tmp4
select t1.Id,t1.Name,t1.StudentNo,t1.Section,t1.ClassCode,
Duplicate_RowNumber
INTO #Duplicatedata
from CTE as c INNER JOIN #Temp1 as t1 ON t1.Id = c.Id
and t1.StudentNo = t1.StudentNo
and c.Duplicate_RowNumber >1
select * from #Duplicatedata
This is going to satisfy both condition as #temp 1 will have both rows for Elle as your join condition is only on ID and Student No.
I added row number column for clarity.
Id Name StudentNo Section ClassCode Duplicate_RowNumber
1 Joe 123 I A1 2
1 Joe 123 I A1 2
2 Harry 113 H X2 2
2 Harry 113 H X2 2
3 Elle 121 E1 J1 2
3 Elle 121 E J1 2
As your Partition is based by Student No and ID, every duplicate row will have 2 or more row numbers.
You can use this approach to delete.
select
ROW_NUMBER() over (partition by Id
, StudentNo
order by Id, StudentNo, section)as Duplicate_RowNumber
, * into #tmp4 from #Temp1
--You can add section in your order as well for consistency purpose.
delete
from #tmp4
output deleted.id, deleted.Name, deleted.StudentNo, deleted.ClassCode,
deleted.Section into #Temp2
where Duplicate_RowNumber > 1
After that it seems like you want to keep one row in your final table and put the other one in you deleted table. For Elle it will delete one of the rows from Final table and keep only one since your partition is not based on section.
To make sure that you delete 1 row from your final table you can use this.
DELETE t
OUTPUT deleted.Id , deleted.Name ,deleted.StudentNo ,deleted.ClassCode
,deleted.Section into #inserted FROM
(select *, row_number() over (Partition by tm.name, tm.studentNo Order by ID,
StudentNo, section ) rownum from #temp1 tm) t
join #Temp2 t2 on t.Id = t2.Id
and t.Name = t2.Name
and t.StudentNo = t2.StudentNo
and t.ClassCode = t2.ClassCode
and t.Section = t2.Section
where t.rownum > 1
If you notice I added this row number, so that it will not two delete the rows from final table, since Joe and Harry has all the matching attributes, and it will delete two rows.
select * from #inserted
Output you get:
Id Name StudentNo ClassCode Section
3 Elle 121 J1 E1
2 Harry 113 X2 H
1 Joe 123 A1 I
Finally you can update final table in this way. #Scenario 2
update TMP
SET ClassCode = NULL, SECTION = NULL
FROM
#Temp1 TMP
JOIN #INSERTED I ON TMP.Id = I.Id
AND TMP.StudentNo = I.StudentNo
SELECT * FROM #Temp1
Final Output:
Id Name StudentNo ClassCode Section
1 Joe 123 NULL NULL
2 Harry 113 NULL NULL
3 Elle 121 NULL NULL
8 Jane 191 A1 E
5 Silva 811 S1 SE
6 Juan 411 S2 SE
7 Carla 431 S2 SE
Please note that I have added scripts and output only for the parts where it required change, and rest part is same script provided by you.