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To: Marc Salomon <marc@library.ucsf.edu>
Cc: postgres@postgres.berkeley.edu
Subject: Re: how to get # of instances of a class 
Date: Fri, 01 Oct 1993 14:08:53 -0700
From: "Caroline M. Paxson" <paxson@postgres.Berkeley.EDU>
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Resent-Date: Fri, 01 Oct 93 14:08:46 PDT


You write:

>I would like to get the number of instances of a class, similar to the
>select count(table) structure in INGRES/SQL.

Use the built-in aggregate "count", as follows:

	retrieve (num = count {myclass.attribute1})

Note that you can't specify myclass.all, because this expands to more
than one attribute, which "count" can't handle.

See the "Aggregate Expressions" subsection of the Postgres manual
(the section is called Introduction(Commands)) for more info.


Carol Paxson
Postgres group, U.C. Berkeley