Question

I’ve got a query that calls a function in its select clause. The function returns a record type. In the calling query, I want to order by one of the fields in the returned record and if possible I’d also like to return the fields of the record as fields of the calling query. To make this clear, here’s a simplified version of the code:

CREATE OR REPLACE FUNCTION getStatus(lastContact timestamptz, lastAlTime timestamptz, lastGps timestamptz, out status varchar, out toelichting varchar, out colorLevel integer)
    RETURNS record AS
    $BODY$
        BEGIN
            status      := 'controle_status_ok';
            toelichting := '';
            colorLevel  := 3;
        END
    $BODY$
        LANGUAGE 'plpgsql' VOLATILE
        COST 100;
ALTER FUNCTION DMI_Controle_getStatus(timestamptz, timestamptz, timestamptz, out varchar, out varchar, out integer) OWNER TO xyz;

Using this function, I want to have a query like this one:

SELECT
    id,
    name,
    getStatus(tabel3.lastcontact, tabel4.lastchanged, tabel5.lastfound) as status
FROM
    tabel1
    left join tabel2 on ...
    left join tabel3 on ...
    left join tabel4 on ...
    left join tabel5 on ...
ORDER BY
    status

Postgres comes with the following error:

ERROR: could not identify an ordering operator for type record

HINT: Use an explicit ordering operator or modify the query.

The question: how should I order by the value of colorLevel that’s been returned by getStatus?

Additional question: can I return the three fields of the getStatus function at fields of the query that calls the getStatus function?

Answer 1

Use

ORDER BY (status).colorlevel

to reference a column of your record type.

As an aside: I used lower case(colorlevel instead of colorLevel) because identifiers are cast to lower case if not double-quoted anyway, and using mixed case identifiers is generally a bad idea in PostgreSQL.

---

As to your additional question, similar syntax requirement. I also use a subquery to optimize the query:

SELECT id
     , name
     , (x.status).status
     , (x.status).toelichting
     , (x.status).colorLevel
FROM   tabel
     , (SELECT getStatus(now(), now(), now()) as status) x
ORDER  BY (x.status).colorlevel

Read about accessing composite types in the manual.

---

Answer after additional input

To use columns from your tables, put it all in the a subquery. I am trying to avoid to call the function multiple times, because that may be expensive.

SELECT
    id,
    name,
    (status).status,
    (status).toelichting,
    (status).colorLevel
FROM (
    SELECT
      id,
      name,
      getStatus(tabel3.lastcontact, tabel4.lastchanged, tabel5.lastfound) as status
    FROM
     tabel1
     left join tabel2 on ...
     left join tabel3 on ...
     left join tabel4 on ...
     left join tabel5 on ...
    ) x
ORDER BY
    (status).colorlevel