[erlang-questions] QLC and mnesia indexes
Mon Nov 5 05:47:34 CET 2007
Is there a way to ask mnesia how many results there are for a given
query without evaluating it (either in QLC or otherwise) if it can
determine the answer entirely from an index?
That is, if I have a set of employees:
And the mnesia table is created like this:
If I wanted to know how many employees started in the last seven
days, I could do:
|| X <- mnesia:table(employee),
X#employee.started_on > SevenDaysAgo ]))).
However, I should also be able to find that out without evaluating
the query at all, since the index on started_on should contain enough
information to figure it out, and given a large number, it can take
much less time. Does QLC or Mnesia have a way to do so?
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