Postgres 12

By using db<>fiddle, you agree to license everything you submit by Creative Commons CC0.

CREATE TABLE tablename (
  Id INTEGER,
  color VARCHAR(4),
  size VARCHAR(6)
);

INSERT INTO tablename
  (Id, color, size)
VALUES
  ('1', 'blue', 'medium'),
  ('2', 'blue', 'medium'),
  ('3', 'blue', 'small'),
  ('4', 'red', 'big');

CREATE TABLE



INSERT 0 4


select t.* from tablename t
where not exists (
  select 1 from tablename 
  where id <> t.id and color = t.color and size = t.size
);


id
color
size


3
blue
small

4
red
big



SELECT 2


select t.Id, t.color, t.size
from (
  select *, count(*) over (partition by color, size) counter
  from tablename
) t  
where t.counter = 1


id
color
size


3
blue
small

4
red
big



SELECT 2


delete from tablename t
where exists (
  select 1 from tablename 
  where id <> t.id and color = t.color and size = t.size
);

select * from tablename

DELETE 2




id
color
size


3
blue
small

4
red
big



SELECT 2