如何在oracle數據庫上使用case..when

Question

我在oracle 11g數據庫上運行sql語句。輸出是像一些加入以下（還有其他列，但重要的列是這些的）

 
id | document  | address 
---+----------------+-------------- 
1 | identity_card | hudson street 
1 | driver_licence | hudson street 
1 | passport  | hudson street 
1 | identity_card | mike street 
1 | driver_licence | mike street 
1 | passport  | mike street 
2 | driver_licence | laura street 
2 | passport  | laura street 
3 | passport  | amy street 
3 | identity_card | bug street 
3 | identity_card | apple street 
3 | passport  | bug street 
4 | driver_licence | 16th street 
5 | identity_card | 21st street 

但是我想這是類似的東西：

 
id | document  | address 
---+----------------+-------------- 
1 | identity_card | hudson street 
1 | identity_card | mike street 
2 | passport  | laura street 
3 | identity_card | bug street 
3 | identity_card | apple street 
4 | driver_licence | 16th street 
5 | identity_card | 21st street 

爲你可能看到我正在查看每個ID，如果ID有identity_card作爲文檔，我拿這行。如果沒有身份證但有護照，我拿那條線，如果沒有身份證和護照，我拿driver_licence。

我該怎麼做這樣的事情？我想我可以使用「case ... when」，但我無法弄清楚如何將「case ... when」應用於我的案例。

在此先感謝！

Answer 1

一種方法是使用dense_rank()：

select t.* 
from (select t.*, 
      dense_rank() over (partition by id 
           order by case when document = 'identity_card' then 1 
               when document = 'passport' then 2 
               when document = 'drivers_license' then 3 
               else 4 
             end) as seqnum 
     from t 
    ) t 
where seqnum = 1; 

Answer 2

要將現有查詢，添加：

, rank() over (partition by id order by case document when 'identity_card' then 1 
                 when 'passport'  then 2 
                 when ...................... 
                 ........................... 
             end) as rnk 

然後，在外部查詢，選擇一切，並添加

where rnk = 1