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;