'How to delete all duplicate records from SQL Table?

Hello I have table name FriendsData that contains duplicate records as shown below 

fID UserID  FriendsID       IsSpecial      CreatedBy
-----------------------------------------------------------------
1   10         11            FALSE            1
2   11          5            FALSE            1
3   10         11            FALSE            1
4    5         25            FALSE            1 
5   10         11            FALSE            1
6   12         11            FALSE            1
7   11          5            FALSE            1
8   10         11            FALSE            1
9   12         11            FALSE            1

I want to remove duplicate combinations rows using MS SQL?
Remove latest duplicate records from MS SQL FriendsData table. here I attached image which highlights duplicate column combinations.

enter image description here

How I can removed all duplicate combinations from SQL table?

sqlsql-servertsqlsql-server-2005duplicates


Solution 1:[1]

It seems counter-intuitive, but you can delete from a common table expression (under certain circumstances). So, I'd do it like so:

with cte as (
  select *, 
     row_number() over (partition by userid, friendsid order by fid) as [rn]
  from FriendsData
)
delete cte where [rn] <> 1

This will keep the record with the lowest fid. If you want something else, change the order by clause in the over clause.

If it's an option, put a uniqueness constraint on the table so you don't have to keep doing this. It doesn't help to bail out a boat if you still have a leak!

Solution 2:[2]

I don't know if the syntax is correct for MS-SQL, but in MySQL, the query would look like:

DELETE FROM FriendsData WHERE fID 
       NOT IN ( SELECT fID FROM FriendsData 
                   GROUP BY UserID, FriendsUserID, IsSpecial, CreatedBy)

In the GROUP BY clause you put the columns you need to be identical in order to consider two records duplicate

Solution 3:[3]

Try this query,

  select * from FriendsData f1, FriendsData f2
  Where f1.fID=f2.fID and f1.UserID  =f2.UserID  and f1.FriendsID  =f2.FriendsID

If it returns you the duplicate rows, then replace Select * by "Delete"

that will solve your problem

Solution 4:[4]

Works in Postgres:

DELETE from "FriendsData" where "fID" in
   (SELECT "fID" from
        (SELECT *, ROW_NUMBER() OVER(PARTITION BY "UserID", "FriendsID" ORDER BY  "fID") as rn
    FROM "FriendsData") as inner1
WHERE rn > 1);

Sources

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Source: Stack Overflow

Solution Source
Solution 1
Solution 2 Tudor Constantin
Solution 3 gmhk
Solution 4 Elikill58

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