[GENERAL] Selecting records with highest timestamp - for a join

[Alexander Farber]

Good evening,

I have a question please on which kind of statement to use -

In a table I store user info coming from social networks (Facebook,
Twitter, ...):

CREATE TABLE words_social (
        sid varchar(255) NOT NULL,

        social integer NOT NULL CHECK (0 <= social AND social <= 6),
        female integer NOT NULL CHECK (female = 0 OR female = 1),
        given  varchar(255) NOT NULL CHECK (given ~ '\S'),
        family varchar(255),
        photo  varchar(255) CHECK (photo ~* '^https?://...'),
        place  varchar(255),
        stamp  integer NOT NULL,  /* HOW TO USE THE LATEST stamp? */

        uid integer NOT NULL REFERENCES words_users ON DELETE CASCADE,
        PRIMARY KEY(sid, social)
);

I.e. a user can have several records in the above table, but I always use
the most recent one (the one with the highest "stamp") to display that user
in my game.

Then I use a custom function to retrieve current games info for a
particular user:

CREATE OR REPLACE FUNCTION words_get_games(in_uid integer)
        RETURNS TABLE (
                out_gid integer,
                out_created integer,
                out_finished integer,
                out_player1 integer,
                out_player2 integer,
                out_played1 integer,
                out_played2 integer,
                out_score1 integer,
                out_score2 integer,
                out_hand1 text,
                out_hand2 text,
                out_letters varchar[15][15],
                out_values integer[15][15],
                out_bid integer,
                out_last_tiles jsonb,
                out_last_score integer
        ) AS
$func$
        SELECT
                g.gid,
                EXTRACT(EPOCH FROM g.created)::int,
                EXTRACT(EPOCH FROM g.finished)::int,
                g.player1,
                g.player2, -- can be NULL
                EXTRACT(EPOCH FROM g.played1)::int,
                EXTRACT(EPOCH FROM g.played2)::int,
                g.score1,
                g.score2,
                ARRAY_TO_STRING(g.hand1, ''),
                REGEXP_REPLACE(ARRAY_TO_STRING(g.hand2, ''), '.', '?', 'g'),
                g.letters,
                g.values,
                g.bid,
                m.tiles,
                m.score
        FROM words_games g LEFT JOIN words_moves m USING(mid)
        WHERE g.player1 = in_uid
        AND (g.finished IS NULL OR g.finished > CURRENT_TIMESTAMP -
INTERVAL '1 day')
        UNION SELECT
                g.gid,
                EXTRACT(EPOCH FROM g.created)::int,
                EXTRACT(EPOCH FROM g.finished)::int,
                g.player2,
                g.player1, -- can not be NULL
                EXTRACT(EPOCH FROM g.played2)::int,
                EXTRACT(EPOCH FROM g.played1)::int,
                g.score2,
                g.score1,
                ARRAY_TO_STRING(g.hand2, ''),
                REGEXP_REPLACE(ARRAY_TO_STRING(g.hand1, ''), '.', '?', 'g'),
                g.letters,
                g.values,
                g.bid,
                m.tiles,
                m.score
        FROM words_games g LEFT JOIN words_moves m USING(mid)
        WHERE g.player2 = in_uid
        AND (g.finished IS NULL OR g.finished > CURRENT_TIMESTAMP -
INTERVAL '1 day');

$func$ LANGUAGE sql;

I would like to extend the above custom function, so that user info (given
and last names, photo) is returned too.

How to approach this problem please, should I use CTE for this?

Thank you for any hints
Alex