>>>I have a table that looks something like this:
>>>
>>>

>>>groupnum          itemnum          quantity
>>>1                  10                  1
>>>2                  10                  1
>>>1                  17                  5
>>>2                  17                  5
>>>1                  23                  2
>>>1                  26                  1
>>>2                  26                  1
>>>1                  27                  3
>>>2                  27                  4
>>>1                  30                  0
>>>2                  30                  0
>>>2                  33                  1
>>>1                  36                  3
>>>2                  36                  5
>>>

>>>
>>>The table isn't really sorted, but we order it this way in queries. As you can see, most itemnums are found in groups 1 and 2, and usually have the same quantity. The user wants a query that returns those itemnums found in both groups, but with different quantities. In the above example, such a query would return:
>>>
>>>

>>>1                  27                  3
>>>2                  27                  4
>>>1                  36                  3
>>>2                  36                  5
>>>

>>>There are probably a few ways to do this, involving sequences of queries, but I wonder what would be the most efficient.
>>Why would

>>1                  17                  5
>>2                  17                  5

not included ?
>>Cetin
>
>I'm not sure if I understand your reply. The purpose of the query is to select pairs where the itemnum is the same, but the quantity is different for groupnum 1 and 2.
"But with different quantities" was the point I missed. Evan already gave the solution.
Cetin