[erlang-questions] Selecting X number of items from Mnesia

Hynek Vychodil <>
Fri Feb 8 10:26:12 CET 2008


Just from qlc manual:

To return just a few answers cursors can be used. The following code returns
no more than five answers using an ETS table for storing the unique answers:


C = qlc:cursor(qlc:q([X || X <- qlc:append(QH1, QH2)],{unique,true})),
R = qlc:next_answers(C, 5),
ok = qlc:delete_cursor(C),
R.

On Feb 8, 2008 9:06 AM, Ulf Wiger <> wrote:

> I'd have to check on how to do it with QLC, but using
> mnesia:select(Tab, MatchSpec, NObjs, Lock), you
> can quite easily pull the N first objects from an
> ordered_set table.
>
> BR,
> Ulf W
>
> 2008/2/8, Dave Bryson <>:
> > I apologize in advance for the newbie question!
> >
> > I'm trying to treat an mnesia table as a FIFO queue. What I'd like to
> > be able to do is pull X number of items off the head of the list
> > returned by a query. There's no conditional values to isolate the
> > records - I just want the top X number of records.  Is there an
> > efficient way to do this with qlc?
> >
> > Thanks in advance!
> >
> > Dave
> > _______________________________________________
> > erlang-questions mailing list
> > 
> > http://www.erlang.org/mailman/listinfo/erlang-questions
> >
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-- 
--Hynek (Pichi) Vychodil
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