[erlang-questions] learning mnesia:select syntax

Håkan Huss <>
Fri Oct 5 09:15:15 CEST 2007


On 10/5/07, Richard Andrews <> wrote:
>
>       MatchHead = #employee{name='$1', sex=male, room_no={'$2', '_'}, _='_'},
>       Guard = [{'>=', '$2', 220},{'<', '$2', 230}],
>       Result = '$1',
>       mnesia:select(employee,[{MatchHead, Guard, [Result]}])
>
> I want to modify this to return {name, sex} of every employee with the same
> Guard.
>
> MatchHead is easy change sex='$3'.
>
> Now what do I do with Result if I want to get back multiple fields.

Result = {{'$1','$3'}},

Perhaps not obvious, but read the match spec information in the ERTS user guide.

Regards,
/Håkan



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