Here are couple of ways to delete duplicate records from a SQL Server table.
--Prepare Sample Data
USE TestDB
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)
Delete all duplicate records by using Common Table Expressions(CTE):
;WITH CTE
AS (
SELECT FirstName,
LastName,
Row_number()
OVER (
PARTITION BY FirstName, LastName
ORDER BY (
SELECT 1) ) AS Rn
FROM dbo.Customer)
DELETE FROM
CTE WHERE EXISTS (SELECT 1 FROM cte t WHERE t.FirstName=cte.FirstName
AND t.LastName=cte.LastName AND rn>1)
Delete all duplicate records by using Group By and Left Join:
DELETE FROM C
FROM dbo.Customer C
LEFT JOIN
(
SELECT FirstName,
LastName,
COUNT(*) AS RecordCnt
FROM dbo.Customer
GROUP BY FirstName,
LastName
HAVING COUNT(*) > 1) DR
ON DR.FirstName=C.FirstName
AND DR.LastName=C.LastName
WHERE DR.FirstName IS NOT NULL
AND DR.LastName IS NOT NULL