Find and delete duplicate friend connections in SQL Server - sql

Question

I need a script to find Member who has a friend connection more than once so it doesn't show their friendship more than once on the website.
The MemberConnection table is as follows:
+----------------------+------------+----------------+
| MemberConnectionID | MemberID | ConnMemberID |
+----------------------+------------+----------------+
| 25 | 33 | 43 |
| 26 | 43 | 33 |
| 27 | 13 | 143 |
| 28 | 143 | 13 |
| 29 | 33 | 43 |
+----------------------+------------+----------------+
As you can see rows 25 and 29 are identical and I need to find these duplicates so they can be deleted.
How can I write a script for this?
Any help that anyone can provide would be greatly appreciated.
Many thanks in advance
neojakey

Answer 1

Try this if you want to leave one connection:
Use this to select connections:
;WITH CTE
AS
(
SELECT
MemberConnectionID,
ROW_NUMBER() OVER (PARTITION BY MemberID, ConnMemberID ORDER BY MemberConnectionID) RN
FROM MemberConnection
)
SELECT
MemberConnectionID
FROM CTE
WHERE RN > 1
or use this to delete from table:
;WITH CTE
AS
(
SELECT
ROW_NUMBER() OVER (PARTITION BY MemberID, ConnMemberID ORDER BY MemberConnectionID) RN
FROM MemberConnection
)
DELETE
FROM CTE
WHERE RN > 1

Answer 2

You can do something like :
SELECT * FROM
(SELECT MemberID,ConnMemberID ,count( MemberID,ConnMemberID ) as c FROM MemberConnection group by MemberID,ConnMemberID ) x
WHERE x.c >1
This will show you all repeated rows.

Answer 3

Using this as a test:
DECLARE #Table AS TABLE
(
MemberConnectionID INT ,
MemberID INT ,
ConMemberID INT
)
INSERT INTO #Table
SELECT 1 ,
2 ,
3
INSERT INTO #Table
SELECT 2 ,
3 ,
4
INSERT INTO #Table
SELECT 3 ,
2 ,
3
Select occurence of member connections
SELECT COUNT(MemberConnectionID) AS Occurence ,
MemberID ,
ConMemberID
FROM #Table
GROUP BY MemberID ,
ConMemberID
Delete Statement
DELETE FROM #Table
FROM #Table t
INNER JOIN ( SELECT MemberID ,
ConMemberID
FROM ( SELECT COUNT(MemberConnectionID) AS Occurence ,
MemberID ,
ConMemberID
FROM #Table
GROUP BY MemberID ,
ConMemberID
) t2
WHERE t2.Occurence > 1
) t3 ON t3.MemberID = T.MemberID
AND t3.ConMemberID = t.ConMemberID

Answer 4

I always use this little query (changed to meet your table).
Delete MemberConnection
from MemberConnection
join
(select max(MemberConnectionId)as CountIt, MemberId, ConnMemberId
from #MemberConnection
group by MemberId, ConnMemberId
having count(1) > 1
) as derived
on MemberConnection.MemberId = derived.MemberId
and MemberConnection.ConnMemberId = derived.ConnMemberId
and CountIt > MemberConnectionId