My problem is this:

I have a table 'history' with columns for ''date_time', 'event', 'sensor'.

The 'event' column may contain 'Calibrated', 'Damaged', 'Repaired'.

Since it is a history, the same sensor may be listed multiple times with a
date for each event.

I want only the most recent calibration event for undamaged sensors.

I am trying to figure out how to winnow out in a single query (no
intermediate
tables) the most recent event for each sensor which has been 'Calibrated' or
'Repaired' not 'Damaged' afterwards.

I had thought it would be so simple. But after much wrangling I seem to be
stumped.

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