Question

Here’s a simplified example of my problem. I have a table where there’s a “Name” column with duplicate entries:

ID    Name
---   ----
 1    AAA
 2    AAA
 3    AAA
 4    BBB
 5    CCC
 6    CCC
 7    DDD
 8    DDD
 9    DDD
10    DDD

Doing a GROUP BY like SELECT Name, COUNT(*) AS [Count] FROM Table GROUP BY Name results in this:

Name  Count
----  -----
AAA   3
BBB   1
CCC   2
DDD   4

I’m only concerned about the duplicates, so I’ll add a HAVING clause, SELECT Name, COUNT(*) AS [Count] FROM Table GROUP BY Name HAVING COUNT(*) > 1:

Name  Count
----  -----
AAA   3
CCC   2
DDD   4

Trivial so far, but now things get tricky: I need a query to get me all the duplicate records, but with a nice incrementing indicator added to the Name column. The result should look something like this:

ID    Name
---   --------
 1    AAA
 2    AAA (2)
 3    AAA (3)
 5    CCC 
 6    CCC (2)
 7    DDD 
 8    DDD (2)
 9    DDD (3)
10    DDD (4)

Note row 4 with “BBB” is excluded, and the first duplicate keeps the original Name.

Using an EXISTS statement gives me all the records I need, but how do I go about creating the new Name value?

SELECT * FROM Table AS T1 
WHERE EXISTS (
    SELECT Name, COUNT(*) AS [Count] 
    FROM Table 
    GROUP BY Name 
    HAVING (COUNT(*) > 1) AND (Name = T1.Name))
ORDER BY Name

I need to create an UPDATE statement that will fix all the duplicates, i.e. change the Name as per this pattern.

Update:
Figured it out now. It was the PARTITION BY clause I was missing.

Answer 1

With Dups As
    (
    Select Id, Name
        , Row_Number() Over ( Partition By Name Order By Id ) As Rnk
    From Table
    )
Select D.Id
    , D.Name + Case
                When D.Rnk > 1 Then ' (' + Cast(D.Rnk As varchar(10)) + ')'
                Else ''
                End As Name
From Dups As D

If you want an update statement you can use pretty much the same structure:

With Dups As
    (
    Select Id, Name
        , Row_Number() Over ( Partition By Name Order By Id ) As Rnk
    From Table
    )
Update Table
Set Name = T.Name + Case
                    When D.Rnk > 1 Then ' (' + Cast(D.Rnk As varchar(10)) + ')'
                    Else ''
                    End
From Table As T
    Join Dups As D
        On D.Id = T.Id