Follow these steps to delete duplicate recodrs
CREATE TABLE dbo.STUDENT
(
StudentID int IDENTITY(1,1) NOT NULL,
Name nvarchar(50) NULL,
RollNumber decimal(10, 2) NULL,
Class nvarchar(50) NULL
)
insert into dbo.STUDENT (Name,RollNumber,Class)values('Andy',100,'MCA')
insert into dbo.STUDENT (Name,RollNumber,Class)values('Andy',100,'MCA')
insert into dbo.STUDENT (Name,RollNumber,Class)values('Bill',200,'BCA')
insert into dbo.STUDENT (Name,RollNumber,Class)values('Bill',200,'BCA')
insert into dbo.STUDENT (Name,RollNumber,Class)values('Bill',200,'BCA')
insert into dbo.STUDENT (Name,RollNumber,Class)values('Chris',300,'MBBS')
Select * from Student

We have a table with duplicate records so remove duplicate records by using ROW_NUMBER()
WITH TempEmp (Name,RollNumber,Class,duplicateRecCount)
AS
(
SELECT Name,RollNumber,Class,ROW_NUMBER() OVER(PARTITION by Name,RollNumber,Class ORDER BY Name)
AS duplicateRecCount
FROM dbo.STUDENT
)
--Now Delete Duplicate Records
DELETE FROM TempEmp WHERE duplicateRecCount > 1
Select * from Student

