Postgres 14

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CREATE TABLE words_users (
    uid SERIAL PRIMARY KEY,
    muted BOOLEAN NOT NULL DEFAULT false
);

CREATE TABLE words_social (
    sid     text     NOT NULL CHECK (sid ~ '\S'),
    social  integer  NOT NULL CHECK (0 < social AND social <= 256),
    given   text     NOT NULL CHECK (given ~ '\S'),
    uid     integer  NOT NULL REFERENCES words_users ON DELETE CASCADE,
    PRIMARY KEY(sid, social)
);

CREATE TABLE words_games (
    gid      SERIAL PRIMARY KEY,
    player1  integer REFERENCES words_users(uid) ON DELETE CASCADE NOT NULL CHECK (player1 <> player2),
    player2  integer REFERENCES words_users(uid) ON DELETE CASCADE
);

CREATE TABLE words_chat (
        cid     BIGSERIAL PRIMARY KEY,
        created timestamptz NOT NULL,
        gid     integer NOT NULL REFERENCES words_games ON DELETE CASCADE,
        uid     integer NOT NULL REFERENCES words_users ON DELETE CASCADE,
        msg     text    NOT NULL
);

-- create 2 users: one is ok, while the other is muted (punished)
INSERT INTO words_users (uid, muted) VALUES (1, false), (2, true);
INSERT INTO words_social (sid, social, given, uid) VALUES ('abc', 100, 'Nice user', 1), ('def', 200, 'Bad user', 2);

-- put these 2 users into a game number 10
INSERT INTO words_games (gid, player1, player2) VALUES (10, 1, 2);

-- start chatting
INSERT INTO words_chat (gid, uid, created, msg) VALUES
(10, 1, CURRENT_TIMESTAMP + INTERVAL '1 min', 'Hi how are you doing?'),
(10, 1, CURRENT_TIMESTAMP + INTERVAL '2 min', 'I am a nice user'),
(10, 2, CURRENT_TIMESTAMP + INTERVAL '3 min', 'F*** ***!!'),
(10, 2, CURRENT_TIMESTAMP + INTERVAL '4 min', 'I am a bad user'),
(10, 1, CURRENT_TIMESTAMP + INTERVAL '5 min','Are you there??');

CREATE OR REPLACE FUNCTION words_get_chat(
                in_gid    integer,
                in_social integer,
                in_sid    text
        ) RETURNS TABLE (
                out_mine  integer,
                out_msg   text
        ) AS
$func$
        WITH myself AS (
            SELECT uid 
            FROM words_social
            WHERE social = in_social
            AND sid = in_sid
            LIMIT 1
        )
        SELECT
                CASE WHEN c.uid = myself.uid THEN 1 ELSE 0 END,
                c.msg
        FROM    words_chat c 
        JOIN    words_games g USING (gid) 
        JOIN    words_users opponent ON (opponent.uid IN (g.player1, g.player2) AND opponent.uid <> myself.uid)
        WHERE   c.gid = in_gid
        -- always show myself my own chat messages
        AND     c.uid = myself.uid 
        -- otherwise only show messages by not muted opponents
        OR      NOT opponent.muted
        ORDER BY c.CREATED ASC;

$func$ LANGUAGE sql;

SELECT words_get_chat(10, 100, 'abc') AS nice_user;

SELECT words_get_chat(10, 200, 'def') AS muted_user;

2 rows affected

2 rows affected

1 rows affected

5 rows affected

ERROR:  missing FROM-clause entry for table "myself"
LINE 64: ...uid IN (g.player1, g.player2) AND opponent.uid <> myself.uid...
                                                              ^