Delete duplicate records from a SQL table without

Question

I have the below table with the below records in it

create table employee
(
 EmpId number,
 EmpName varchar2(10),
 EmpSSN varchar2(11)
);

insert into employee values(1, 'Jack', '555-55-5555');
insert into employee values (2, 'Joe', '555-56-5555');
insert into employee values (3, 'Fred', '555-57-5555');
insert into employee values (4, 'Mike', '555-58-5555');
insert into employee values (5, 'Cathy', '555-59-5555');
insert into employee values (6, 'Lisa', '555-70-5555');
insert into employee values (1, 'Jack', '555-55-5555');
insert into employee values (4, 'Mike', '555-58-5555');
insert into employee values (5, 'Cathy', '555-59-5555');
insert into employee values (6 ,'Lisa', '555-70-5555');
insert into employee values (5, 'Cathy', '555-59-5555');
insert into employee values (6, 'Lisa', '555-70-5555');

I dont have any primary key in this table .But i have the above records in my table already. I want to remove the duplicate records which has the same value in EmpId and EmpSSN fields.

Ex : Emp id 5

Can any one help me to frame a query to delete those duplicate records

Thanks in advance

Answer 1

delete sub from (select ROW_NUMBER() OVer(Partition by empid order by empid)cnt from employee)sub where sub.cnt>1

Answer 2

select distinct * into newtablename from oldtablename

Now, the newtablename will have no duplicate records.

Simply change the table name(newtablename) by pressing F2 in object explorer in sql server.

Answer 3

no ID, no rowcount() or no temp table needed....

WHILE 
  (
     SELECT  COUNT(*) 
     FROM TBLEMP  
     WHERE EMPNO 
            IN (SELECT empno  from tblemp group by empno having count(empno)>1)) > 1 


DELETE top(1)  
FROM TBLEMP 
WHERE EMPNO IN (SELECT empno  from tblemp group by empno having count(empno)>1)

Answer 4

With duplicates

As
(Select *, ROW_NUMBER() Over (PARTITION by EmpID,EmpSSN Order by EmpID,EmpSSN) as Duplicate From Employee)

delete From duplicates

Where Duplicate > 1 ;

This will update Table and remove all duplicates from the Table!

Answer 5

If you don't want to create a new primary key you can use the TOP command in SQL Server:

declare @ID int
while EXISTS(select count(*) from Employee group by EmpId having count(*)> 1)
begin
    select top 1 @ID = EmpId
    from Employee 
    group by EmpId
    having count(*) > 1

    DELETE TOP(1) FROM Employee WHERE EmpId = @ID
end

Answer 6

ALTER IGNORE TABLE test
           ADD UNIQUE INDEX 'test' ('b'); 

@ here 'b' is column name to uniqueness, @ here 'test' is index name.