>>Part 1, Part 2
>>1 1
>>1 2
>>2 1
>>1 3
>>2 2
>>3 1
>>1 4
>>3 2
>>
>>What is the best way to solve this? I think I need a generator which
>>gets the last number (part 2) there is for a given entry (part1) and
>>increment that value.

My suggestion would be to store current timestamp as part 2
but only if the part 2 sequence is supposed to represent the
creation order of the entries.

You can then (if required) generate an ordinal contiguous
number sequence however apart for listing re-ordering
I have yet to find a need for this.

Even in the case of listing re-ordering (MOVEUP/MOVEDOWN)
numbers do not have to be contiguous and a single
sequence (such as that created by a generator) will do the trick.

Jacqui