delete from test_duplicate
where id not in(
select min(id)
        from TEST_DUPLICATE
        group by EmpId ) 

WITH CTE(N) AS(SELECT ROW_NUMBER()OVER(PARTITION BY EmpId ORDER BY id) FROM test_duplicate)
DELETE CTE WHERE N>1;

WITH CTE AS(SELECT N=ROW_NUMBER()OVER(PARTITION BY EmpId ORDER BY id),* FROM test_duplicate)
SELECT * FROM CTE WHERE N>1;

USE [tempdb]
GO
CREATE TABLE [dbo].[TD1](
	[Id] [int] IDENTITY(1,1) NOT NULL,
	[EmpId] [int] NULL,
	[ObjId] [int] NULL,
	[PostId] [int] NULL,
	[DepId] [int] NULL
) ON [PRIMARY]

GO
INSERT [dbo].[TD1] ([EmpId], [ObjId], [PostId], [DepId]) VALUES (1, 1, 1, 1)
INSERT [dbo].[TD1] ([EmpId], [ObjId], [PostId], [DepId]) VALUES (1, 2, 1, 1)
INSERT [dbo].[TD1] ([EmpId], [ObjId], [PostId], [DepId]) VALUES (2, 1, 1, 1)
INSERT [dbo].[TD1] ([EmpId], [ObjId], [PostId], [DepId]) VALUES (3, 1, 1, 1)
INSERT [dbo].[TD1] ([EmpId], [ObjId], [PostId], [DepId]) VALUES (3, 2, 1, 1)
INSERT [dbo].[TD1] ([EmpId], [ObjId], [PostId], [DepId]) VALUES (4, 1, 1, 1)
INSERT [dbo].[TD1] ([EmpId], [ObjId], [PostId], [DepId]) VALUES (2, 2, 2, 2)
INSERT [dbo].[TD1] ([EmpId], [ObjId], [PostId], [DepId]) VALUES (5, 2, 1, 1)
GO
select *
from TD1

select *
from TD1
where Id in(
select min(Id)
        from TD1
        group by EmpId ) 

select top(1) with TIES *
from TD1
order by EmpId
;
WITH CTE AS(SELECT N=ROW_NUMBER()OVER(PARTITION BY EmpId ORDER BY id),* FROM TD1)
SELECT * FROM CTE WHERE N>1;
DROP TABLE [dbo].[TD1]
GO

select	top(1) with ties *
from	dbo.TD1
order by dense_rank() over (partition by [EmpId] order by ID)