newbie : writing an efficient query

I have a table t1 : time1 unique, qty
Entries : (1, 10) (2, 20) (3,30) (32,20)

I want to find out the time1 values where qty is the same.

select a1.time1, a2.time1
from t1 a1, t1 a2
where a1.qty = a2.qty and a1.time1 <> a2.time1 -- and a1.time1 > a2.time1

produces output :

32     2
2      32

But I want just one line in the output. Uncommenting the clause achieves the effect but somehow it seems a contrived way of getting the desired result. Besides if unique key is on (date + time), it would make the task more difficult. I think a more logical way would help me write the query efficiently whether the unique key was on a single field or multiple fields.

Please advise about a logical way of writing the query. Received on Thu Aug 03 2006 - 18:49:28 CDT