SQL Server : find duplicates in a table based on values in a single column

问题

I have a SQL Server table with the following fields and sample data:

ID   employeename
1    Jane
2    Peter
3    David
4    Jane
5    Peter
6    Jane

The ID column has unique values for each row.

The employeename column has duplicates.

I want to be able to find duplicates based on the employeename column and list the IDs of the duplicates next to them separated by commas.

Output expected for above sample data:

employeename   IDs
Jane           1,4,6
Peter          2,5

There are other columns in the table that I do no want to consider for this query.

Thanks for all your help!

回答1:

select
 employeename,
 IDs = STUFF((SELECT ','+ CAST(e2.[ID] AS VARCHAR(10)) 
  FROM emp e2
  WHERE e2.employeename = e1.employeename
  For XML PATH('')
 ),1,1,'')
FROM emp e1
GROUP BY employeename having COUNT(*) > 1

SQL Fiddler

回答2:

Here is a Northwind example:

Use Northwind
GO

SELECT
   ord1.CustomerID,
   OrderIdList = substring((SELECT ( ', ' + convert(varchar(16) , OrderID) )
                           FROM [dbo].[Orders] ord2
                           WHERE ord1.CustomerID = ord2.CustomerID
                           ORDER BY 
                              CustomerID,
                              OrderID
                           FOR XML PATH( '' )
                          ), 3, 1000 )FROM [dbo].[Orders] ord1
GROUP BY CustomerID

来源：https://stackoverflow.com/questions/16525064/sql-server-find-duplicates-in-a-table-based-on-values-in-a-single-column