Remove duplicate rows in Postgres - sql

Question

I have two tables:
Employee:
ID
Name
Surname
143
Amy
Flowers
245
Natasha
Smith
365
John
Alexander
445
Natasha
Smith
565
Monica
Withhouse
644
Amy
Flowers
1023
Amy
Alexander
And employee_details:
ID
Employee_id
Document_numer
1
644
XXXXXXXXX
2
245
XXXXXX
3
365
XXXXXX
I need to remove duplicate records that are in the Employee table and that are not related to the employee_details table. In the example data, I would like to delete the employee doublet with the id 143 and 445.
And I must admit that I have no idea how to do it.Could you give me a hint?
The base is postgres

Answer 1

Delete from Employee
Where id not in (
Select Employee_id
from employee_details
)
and name in (
Select name
from Employee
Group by name having count(name) > 1
)

Answer 2

Though the question is already answered I am adding two different answers here using cte.
create table Employee(ID int, Name varchar(50), Surname varchar(50));
insert into Employee values(143, 'Amy', 'Flowers');
insert into Employee values(245, 'Natasha', 'Smith');
insert into Employee values(365, 'John', 'Alexander');
insert into Employee values(445, 'Natasha', 'Smith');
insert into Employee values(565, 'Monica', 'Withhouse');
insert into Employee values(644, 'Amy', 'Flowers');
insert into Employee values(1023, 'Amy', 'Alexander');
create table employee_details ( ID int, Employee_id int, Document_numer varchar(50));
insert into employee_details values(1, 644, 'XXXXXXXXX');
insert into employee_details values(2, 245, 'XXXXXX');
insert into employee_details values(3, 365, 'XXXXXX');
Delete query 1:
with duplicate_employees as
(
select * , count(id)over(partition by name,surname) duplicate_count from Employee
)
delete from Employee where id in(
select id from duplicate_employees de
where duplicate_count >1
and not exists
(
select 1 from employee_details e where e.Employee_id = de.ID
)
)
select * from employee
Output:
id
name
surname
245
Natasha
Smith
365
John
Alexander
565
Monica
Withhouse
644
Amy
Flowers
1023
Amy
Alexander
db<>fiddle here
Delete query 2:
with cte as
(
Select *, count(*)over(partition by name,surname) duplicate_count,
(case when exists
(
select 1 from employee_details ed where ed.Employee_id = e.ID
)
then 1 else 0 end) exist_in_details
from Employee e
)
delete from Employee where id in (select id from cte where duplicate_count>1 and exist_in_details=0 )
select * from Employee
Output:
id
name
surname
245
Natasha
Smith
365
John
Alexander
565
Monica
Withhouse
644
Amy
Flowers
1023
Amy
Alexander
db<>fiddle here