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SELECT t.*
FROM table t
WHERE t.start <= @probeDate AND
    ( t.finish => @probeDate OR
      t.finish IS NULL )

SELECT t.*
FROM table t
WHERE t.start <= @probeDate AND
    ( t.finish >= @probeDate OR
      t.finish IS NULL )

SELECT t.*
FROM table t
WHERE t.start <= probeDate AND
    ( t.finish => probaDate OR
      t.finish IS NULL )

SELECT t.*
FROM table t
WHERE t.start <= @probeDate AND
    ( t.finish => @probeDate OR
      t.finish IS NULL )

PS.: Don't worry about the internal integrity of NodeList and Node (checking for invalid nodes, invalid min and max datetimes, checking overlaps, etc.) — this is just a quick and dirty concept. I'm primarily interested in the search algorithm in NodeList::find() and consequently NodeList::binarySearch().