Finding duplicates using SQL

Heres a query that helps you find the duplicates and updates all duplicate records with error description as duplicate record leaving one record
If the primary key id is a integer based identity column, if not create a temp table with same structure and additional identity column, and use the identity column instead of primary key id

UPDATE TableName SET ErrorDescription = 'Duplicate record' WHERE PrimaryKeyId > (SELECT MIN(PrimaryKeyId) FROM TableName CheckDuplicate WHERE (CheckDuplicate.Code = TableName.Code OR CheckDuplicate.Name = TableName.Name)) AND ErrorDescription IS NULL

If records were

PrimaryKeyId	Code	Name	ErrorDescription
1	CD1	Name 1
2	CD2	Name 2
3	CD1	Name 3
4	CD4	Name 1

They become

PrimaryKeyId	Code	Name	ErrorDescription
1	CD1	Name 1
2	CD2	Name 2
3	CD1	Name 3	Duplicate record
4	CD4	Name 1	Duplicate record