CREATE TABLE a(a_id int , c_id int, amt int);

INSERT INTO a VALUES(1,1,10);
INSERT INTO a VALUES(2,1,-20);
INSERT INTO a VALUES(3,2,-10);
INSERT INTO a VALUES(4,2,10);
INSERT INTO a VALUES(5,3,100);
INSERT INTO a VALUES(6,3,10);
INSERT INTO a VALUES(7,4,10);
INSERT INTO a VALUES(8,4,0);
INSERT INTO a VALUES(9,5,10);
INSERT INTO a VALUES(10,6,0);

select c_id
from a
group by c_id
having amt>0

select c_id, sum(amt) amt
from a
group by c_id
having sum(amt)>0

select distinct a1.c_id from a a1
   where 0 < all(select amt from a a2 where a2.c_id = a1.c_id)

select distinct a1.c_id from a a1
where a1.c_id not in (select a2.c_id from a a2 where a2.amt <= 0)

select distinct a1.c_id from a a1
where not exists(select amt from a a2 where a2.c_id = a1.c_id and a2.amt <=0)

select c_id
from a
group by c_id
having amt>0

select c_id
from a
group by c_id
having min(amt)>0