> a) the finish is after the start
well, finish > start
> b) two allocations for a single vehicle don't overlap.
this one is a bit tricky !
- Check that there is no allocation in the table whose time period start,
end includes either the start of the end of the reservation to insert, and
that the time period of the reservation to insert does not contain either
the start or end of any reservation in the table.
This is 4 selects, playing with order by limit 1 and indexes, it will be
fast.