透视数据并将单列放入具有关联行的多列中

Posted 2023-03-31

【中文标题】透视数据并将单列放入具有关联行的多列中

【英文标题】：Pivoting Data and putting single column into multiple columns with associated rows

【发布时间】：2020-03-17 17:32:35

【问题描述】：

我在 Amazon Redshift (PostgreSQL) 中有如下所示的数据：

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  |         |  

我已尝试执行以下操作并取得了一些成功。为了创建我的 3 个用户名列，我使用带有 WHERE 条件的连接将数据从视图中提取出来，次数不限。但是，我不禁觉得有一种比我现在这样做的方式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
    ...

【参考方案1】：

从您现有的子查询开始，一种方法使用条件聚合而不是连接：

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;