How to delete all duplicate records from SQL Table

问题:

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.

How I can removed all duplicate combinations from SQL table?

回答1:

Try this

DELETE
FROM FriendsData 
WHERE fID NOT IN
(
SELECT MIN(fID)
FROM FriendsData 
GROUP BY UserID, FriendsID)

See here

Or here is more ways to do what you want

Hope this helps

回答2:

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!

回答3:

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

回答4:

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