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

How can I frame a query to delete those duplicate records?

Answer 1

Add a Primary Key (code below)

Run the correct delete (code below)

Consider WHY you woudln’t want to keep that primary key.

---

Assuming MSSQL or compatible:

ALTER TABLE Employee ADD EmployeeID int identity(1,1) PRIMARY KEY;

WHILE EXISTS (SELECT COUNT(*) FROM Employee GROUP BY EmpID, EmpSSN HAVING COUNT(*) > 1)
BEGIN
    DELETE FROM Employee WHERE EmployeeID IN 
    (
        SELECT MIN(EmployeeID) as [DeleteID]
        FROM Employee
        GROUP BY EmpID, EmpSSN
        HAVING COUNT(*) > 1
    )
END