DROP TABLE IF EXISTS tmp1;
CREATE TABLE tmp1(
name text,
num int
);

INSERT INTO tmp1 (name,num) VALUES
('abc',1),
('fegerg',2),
('regegeg',8),
('ergegerg',3),
('ergegge',4),
('bbdfberb',2),
('regerg',8),
('grgerg',5),
('kmkiji',1)
;

SELECT * FROM tmp1 WHERE num IN (SELECT num FROM tmp1 GROUP BY num HAVING count(num)>1);

   name   | num
----------+-----
 abc      |   1
 fegerg   |   2
 regegeg  |   8
 bbdfberb |   2
 regerg   |   8
 kmkiji   |   1
(6 строк)