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Date: Fri, 16 Oct 2009 22:27:27 -0400
Message-ID: <302670f20910161927h688e13e7qd096e63e68b7ae6c@mail.gmail.com>
Subject: Efficiency in Multiple Queries of Same Table in a PL/PgSQL Function
From: Gary Chambers <gwchamb@gmail.com>
To: pgsql-sql@postgresql.org
Content-Type: text/plain; charset=ISO-8859-1

All...

In the poly_example function below, I am emulating an actual
requirement by querying the same table three (3) times in order to
derive a solution to a problem.  Is this the best or most efficient
and effective way to implement this?  The table (which consists of
only five (5) FLOAT8 columns) I'm querying contains less than 50 rows.
 Thanks in advance for any insight or criticisms you offer.

CREATE OR REPLACE FUNCTION poly_example() RETURNS SETOF FLOAT8 AS
$poly_example$
DECLARE
    term blah%ROWTYPE;
    sigma_l FLOAT8 := 0.0;
    sigma_b FLOAT8 := 0.0;
    sigma_r FLOAT8 := 0.0;

BEGIN
    FOR term in SELECT * FROM blah LOOP
        sigma_l := sigma_l + (RANDOM() * 100) * (term.i * term.i) +
                RANDOM() * (term.j * term.j) + term.k;
    END LOOP;

    FOR term in SELECT * FROM blah LOOP
        sigma_b := sigma_b + (RANDOM() * 53) * (term.i * term.i) +
                (RANDOM() * 5) * (term.j * term.j) + term.k;
    END LOOP;

    FOR term in SELECT * FROM blah LOOP
        sigma_r := sigma_r + 96.232234 * (term.i * term.i) +
                0.32322325 * (term.j * term.j) + term.k;
    END LOOP;

    RETURN NEXT sigma_l + sigma_b + sigma_r;
END;
$poly_example$ LANGUAGE plpgsql STRICT IMMUTABLE;

-- Gary Chambers

/* Nothing fancy and nothing Microsoft! */