CREATE OR REPLACE FUNCTION readMessage(messageFor INT, qid INT = NULL, ctxt INT = NULL, messageFrom INT = NULL, byTimeStamp BOOLEAN = FALSE)
RETURNS SETOF message
AS $$
DECLARE
    sql varchar;
BEGIN
    sql := 'SELECT * FROM message WHERE (receiver_id IS NULL OR receiver_id = $1)';
    IF qid IS NOT NULL THEN
        sql := sql || ' AND queue_id = $2';
    END IF;
    IF ctxt IS NOT NULL THEN
        sql := sql || ' AND context = $3';
    ELSE
        sql := sql || ' AND context IS NULL';
    END IF;

    IF $4 IS NOT NULL THEN
        sql := sql || ' AND sender_id = $4';
    END IF;

    sql := sql || ' ORDER BY';
    IF byTimeStamp THEN
        sql := sql || ' arrive_time ASC';
    ELSE
        sql := sql || ' priority DESC';
    END IF;

    sql := sql || ' LIMIT 1';
    RETURN QUERY EXECUTE sql
    USING messageFor, qid, ctxt, messageFrom;
END;
$$
LANGUAGE plpgsql;

Connection con;
PreparedStatement ps = con.prepareStatement("select readMessage(1, 1, 1, 1, true))";
ResultSet rs = ps.executeQuery();
rs.getInt(<column-name>)

rs.getInt(<column-index>)

CREATE TABLE test.child (
    id    integer,
    p_id1 integer,
    p_id2 integer
);

CREATE OR REPLACE FUNCTION named_cols()
RETURNS SETOF test.child
LANGUAGE sql
AS $$                                                                                                                                                 SELECT 0, 12, 23;                                                                                                                                                                                                 $$;


SELECT named_cols();
 named_cols
────────────
 (0,12,23)


SELECT * FROM named_cols();
 id │ p_id1 │ p_id2
────┼───────┼───────
  0 │    12 │    23

SELECT * FROM [FUNCTION_NAME()]