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From: carl@eleazar.dartmouth.edu (Carl Pedersen)
Newsgroups: comp.databases
Subject: Time related records
Message-ID: <22947@dartvax.Dartmouth.EDU>
Date: 28 Jun 90 17:08:51 GMT
References: <1082@kirk.nmg.bu.oz>
Sender: news@dartvax.Dartmouth.EDU
Organization: Dartmouth College, Hanover, NH
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My attempt to mail this bounced, so here is my reply to Cameron
Stevenson.

If you have a unique id for the key and for each person, and the
time the key was given to the person, then these three items
together comprise a unique key for the table.

Why not just leave the old records there?

The person who has the key now is the one who took it out most
recently.

   select who from t where key_id = 12345 and checked_out =
     (select max(checked_out) from t where key_id = 12345);

You may want to keep track of the times when the key is not
checked out to anyone.  In that case, if storage isn't a big
issue, you could just have a special "person" who would "hold"
all keys that are not checked out.