[georgismilyanov]

Exactly.

There are four types of meeting: mouse 1 entered -> mouse 2 entered -> mouse 2 left -> mouse 1 left; mouse 1 entered -> mouse 2 entered -> mouse 1 left -> mouse 2 left; mouse 2 entered -> mouse 1 entered -> mouse 1 left -> mouse 2 left; mouse 2 entered -> mouse 1 entered -> mouse 2 left -> mouse 1 left.

Then the meeting record contains the times the two were together and the duration of this.

The dumb approach is very slow. Would it be a good idea to read all stay results in Scala (or whatever) and try to do the searching in memory, completely eliminating th db? But then the comparisons would be more expensive...