How to Find duplicate records in a SQL Server Table

CREATE TABLE dbo.Customer( ID INT, FirstName VARCHAR(100),LastName VARCHAR(100),Age INT)

GO

INSERT INTO dbo.Customer

 VALUES(1,'Aamir','Shahzad',34)
,(1,'Aamir','Shahzad',34)
,(2,'Raza','M',32)
,(3,'Sukhjeet','Singh',27)
,(4,'Sukhjeet','Singh',28)

SELECT * FROM  dbo.Customer

Find duplicate records by using Group by:

SELECT FirstName,
            LastName,
            COUNT(*) AS RecordCnt
    FROM   dbo.Customer
    GROUP  BY FirstName,
            LastName
    HAVING COUNT(*) > 1