create table idtest (id1 integer, id2 integer);

insert into idtest values('1','1');
insert into idtest values('1','2');
insert into idtest values('2','1');
insert into idtest values('3','1');
insert into idtest values('3','2');

select * from idtest;
+ ------+------+
 
| id1  | id2  |
+ ------+------+
 
|     1  |     1  |
|     1  |     2  |
|     2  |     1  |
|     3  |     1  |
|     3  |     2  |
+ ------+------+
 
 5  rows in set ( 0 . 00  sec)

SELECT a.id1
FROM idtest a, idtest b
WHERE
a.id1=b.id1
AND
a.id2= 1 
AND
b.id2= 2 ;
+ ------+
 
| id1  |
+ ------+
 
|     1  |
|     3  |
+ ------+
 

SELECT t_1.id1
FROM idtest t_1, idtest t_2, ...., idtest t_n
WHERE
(
  t_1.id1=t_2.id1
  AND
  ...
  AND
  t_1.id1=t_n.id1
)
AND
(
  t_1.id2= 1 
  AND
  t_2.id2= 2 
  ...
  AND
  t_n.id2=n
);

CREATE TEMPORARY TABLE aaa (id1 int, id2 int);
INSERT INTO aaa SELECT id1, id2 FROM idtest GROUP BY id1, id2;
SELECT id1, count(*) FROM aaa GROUP BY id1 HAVING count(*)> 1 ;
DROP aaa;