Thread: comparison trigger function

Hi All,

I just built the trigger function below to gaurantee that the width entered in
a table is always less than the length.  It seems to work but I would like to
know if there is a better (more concise, faster) way of providing this
functionality.

Kind Regards,
Keith

-- Function: tf_width_lt_length()

-- DROP FUNCTION tf_width_lt_length();

CREATE OR REPLACE FUNCTION tf_width_lt_length()
  RETURNS "trigger" AS
$BODY$
   DECLARE
      v_quantity FLOAT4;
   BEGIN
--    If width is greater than length reverse their values.
      IF NEW.width_in > NEW.length_in THEN
         v_quantity := NEW.width_in;
         NEW.width_in := NEW.length_in;
         NEW.length_in := v_quantity;
      END IF;
      RETURN NEW;
   END;
$BODY$
  LANGUAGE 'plpgsql' VOLATILE;

ALTER FUNCTION tf_width_lt_length() OWNER TO postgres;
GRANT EXECUTE ON FUNCTION tf_width_lt_length() TO postgres;
GRANT EXECUTE ON FUNCTION tf_width_lt_length() TO public;

-- Trigger: tgr_width_lt_length on tbl_data

-- DROP TRIGGER tgr_width_lt_length ON tbl_data

CREATE TRIGGER tgr_width_lt_length
  BEFORE INSERT OR UPDATE
  ON tbl_data
  FOR EACH ROW
  EXECUTE PROCEDURE tf_width_lt_length();

Not really. You can require this with a table constraint,

CREATE TABLE boxes (
    length NOT NULL,
    width NOT NULL,
    CONSTRAINT shape CHECK (length > width)
);

But that won't automatically switch them.

Keith Worthington wrote:
> Hi All,
>
> I just built the trigger function below to gaurantee that the width entered in
> a table is always less than the length.  It seems to work but I would like to
> know if there is a better (more concise, faster) way of providing this
> functionality.
>
> Kind Regards,
> Keith
>
> -- Function: tf_width_lt_length()
>
> -- DROP FUNCTION tf_width_lt_length();
>
> CREATE OR REPLACE FUNCTION tf_width_lt_length()
>   RETURNS "trigger" AS
> $BODY$
>    DECLARE
>       v_quantity FLOAT4;
>    BEGIN
> --    If width is greater than length reverse their values.
>       IF NEW.width_in > NEW.length_in THEN
>          v_quantity := NEW.width_in;
>          NEW.width_in := NEW.length_in;
>          NEW.length_in := v_quantity;
>       END IF;
>       RETURN NEW;
>    END;
> $BODY$
>   LANGUAGE 'plpgsql' VOLATILE;
>
> ALTER FUNCTION tf_width_lt_length() OWNER TO postgres;
> GRANT EXECUTE ON FUNCTION tf_width_lt_length() TO postgres;
> GRANT EXECUTE ON FUNCTION tf_width_lt_length() TO public;
>
> -- Trigger: tgr_width_lt_length on tbl_data
>
> -- DROP TRIGGER tgr_width_lt_length ON tbl_data
>
> CREATE TRIGGER tgr_width_lt_length
>   BEFORE INSERT OR UPDATE
>   ON tbl_data
>   FOR EACH ROW
>   EXECUTE PROCEDURE tf_width_lt_length();
>
> ---------------------------(end of broadcast)---------------------------
> TIP 8: explain analyze is your friend