SQL Server clears fully duplicated data only the first of the duplicate data is preserved _mssql

--Creating a test table create 
table [dbo].[ Testtab] ( 
[ID] [nchar] (a) null, 
[name] [nchar] (a) null 
); 
--Inserts test data into the test table insert into 
testtab values (' 1 ', ' 1 '); 
INSERT into Testtab values (' 1 ', ' 1 '); 
INSERT into Testtab values (' 2 ', ' 2 '); 
INSERT into Testtab values (' 2 ', ' 2 '); 
INSERT into Testtab values (' 3 ', ' 3 '); 
INSERT into Testtab values (' 3 ', ' 3 '); 

--Create a temporary table and insert the data in the test table testtab into the temporary table and add the Id:autoid 
Select Identity (int,1,1) as Autoid, * into #Tmp from Testtab 
- Deletes the duplicate data in the temporary table #tmp according to Autoid, leaving only the first delete in each set of duplicate data 
#Tmp where autoid in (select Max (autoid) to #Tmp Group by ID); 
--Clears all data in the Testtab table to 
delete testtab; 
-Inserts the processed data from the #tmp table into the Testtab table into the 
testtab select Id,name from #Tmp; 
--Delete temporary table #tmp 
drop table #Tmp;