[erlang-questions] Mnesia - select with placeholder in table key

[Ulf Wiger]

If the key position is unbound, mnesia will check if any indexed position is bound, and if so, use the first such value for an index lookup. It then uses match_spec_run() on the result.

BR,
Ulf W

Ulf Wiger, Feuerlabs, Inc.
http://www.feuerlabs.com

26 maj 2013 kl. 22:46 skrev John Doe <donpedrothird@REDACTED>:

> If I use select when the key is tuple with placeholders, something like this (taken from erlang docs and changed a bit):
> MatchHead = #person{name = {'$1', "K", "Jameson"}, sex = '$2', _ = '_'},
> Result = '$2',
> mnesia:select(Tab,[{MatchHead, [], [Result]}])
>  where name is the table key
> will mnesia do full table scan in this case? Or it will be smarter and select all records with key matching {_, "K", "Jameson"} using index somehow? 
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