Finding Duplicates on a Column Subset with Detail

Students with same name and date of birth

WITH CTE (StudentId, Fname, LName, DOB, RowCnt)
as (
SELECT StudentId, FirstName, LastName, DateOfBirth as DOB, SUM(1) OVER (Partition By FirstName, LastName, DateOfBirth) as RowCnt
FROM tblStudent
)
SELECT * from CTE where RowCnt > 1
ORDER BY DOB, LName

This example uses a Common Table Expression and a Window Function to show all duplicate rows (on a subset of columns) side by side.

Remarks

To select rows with out duplicates change the WHERE clause to "RowCnt = 1"

To select one row from each set use Rank() instead of Sum() and change the outer WHERE clause to select rows with Rank() = 1