postgresql行转列并拼接字符串

有这样一张表：

select * from liutest order by 1;

id |   kw   
----+--------
  1 | big
  1 | hello
  2 | oracle
  2 | small
  2 | apple
  3 | shit
(6 rows)

我想按id把kw拼接成一个字符串，在网上查到一种方法：

select id,
array_to_string
        (
        ARRAY   (
                SELECT  kw
                FROM    liutest gi
                WHERE   gi.id = gd.id
                ),
        ', '
        ) AS group_concat
FROM    liutest gd
ORDER BY
        id;