Sql 数据透视并将单列放入具有关联行的多列

我在Amazon Redshift（PostgreSQL）中有如下数据：

acct    | id_cd   | username
acc1    |123      | kchalm  
acc1    |123      | rsmith  
acc1    |123      | ehamon  
acc1    |123      | ljenin  
acc2    |234      | kchalm  
acc2    |234      | rtheis  
acc3    |345      | jbalvi  
acc3    |345      | twoods  
acc3    |345      | jli  
acc4    |345      | rshant

我需要它看起来像这样

acct    | id_cd   |username1|username2|username3
acc1    |123      | kchalm  | rsmith  | ehamon  
acc1    |123      | ljenin  |         |   
acc2    |234      | kchalm  | rtheis  |
acc3    |345      | jbalvi  | twoods  | jli  
acc4    |345      | rshant  |         |  

我试着做了以下几件事，取得了一些成功。为了创建我的3个用户名列，我使用带有WHERE条件的联接多次从视图中提取数据。然而，我忍不住觉得有一种比我现在这样做更好的方法来自动化这个过程。有什么建议吗

    SELECT
    ut.acct,
    ut.id_code,
    ut.username,
    ROW_NUMBER() OVER(PARTITION BY ut.account_code
ORDER BY
    ut.username DESC) AS row_num
FROM
    orig_user_table ut ;

select
    a.acct
    ,a.id_cd
    ,a.username1
    ,b.username2
FROM
    (
    SELECT
        acct,
        id_cd,
        username AS username1
    FROM
        vw_user_table_nums
    WHERE
        row_num = 1) a
LEFT JOIN (
    SELECT
        acct,
        username AS username2
    FROM
        vw_user_table_nums
    WHERE
        row_num = 2) b ON
    a.acct = b.acct
    ...

---

从现有子查询开始，有一种方法使用条件聚合而不是联接：

select
    acct,
    id_code,
    max(case when rn = 1 then username end) username1,
    max(case when rn = 2 then username end) username2,
    max(case when rn = 3 then username end) username3
from (
    select
        ut.*,
        row_number() over(partition by ut.account_code order by ut.username desc) as rn
    from orig_user_table ut 
) t
group by acct, id_code
order by acct, id_code;