樞軸多行

Question

我有類似如下的表：

id key str_val date_val  num_val 
1  A  a 
1  B  b 
1  C     2012-01-01 
1  D        1 
2  A  c 
2  E  d 
2  C     2012-01-02 
2  D        2 

我需要它看起來像：

id A  B  C    D  E 
1  a  b  2012-01-01 1 
2  c    2012-01-02 2  d 

基本上，每個關鍵需求，成爲它自己的列

我試過並且未能有效地使用PIVOT命令，而我正在試圖用case語句來完成此操作。即

select 
    id, 
    case key 
     when 'A' 
     then str_val 
    end as A, 
    case key 
     when 'C' 
     then date_val 
    end as C 
    --etc. 
from test_table 

但是我不知道如何在運行後組合表格行。我被困在：

id A  B  C    D  E 
1  a 
1   b 
1     2012-01-01 
1         1 

任何想法或輸入可以幫助我嗎？提前致謝。

Answer 1

你是那裏的方式90％ ：

with cte as (
    select 
     id, 
     case [key] 
      when 'A' 
      then str_val 
     end as A, 
     case [key] 
      when 'B' 
      then str_val 
     end as B, 
     case [key] 
      when 'C' 
      then date_val 
     end as C, 
     case [key] 
      when 'D' 
      then num_val 
     end as D, 
     case [key] 
      when 'E' 
      then str_val 
     end as E 
    from test_table 
) 
select id, max(A) as A, max(B) as B, max(C) as C, max(D) as D, max(E) as E 
from cte 
group by id 

Answer 2

只要ID和密鑰是每桌一個獨特的組合，那麼你可以寫你的查詢，如：

SELECT ta.str_val as A, 
     tb.str_val as B, 
     tc.date_val as C, 
     td.num_val as D, 
     te.str_val as E 
FROM (SELECT DISTINCT id FROM test_table) ids 
LEFT JOIN test_table ta ON ids.id = ta.id AND ta.key = 'A' 
LEFT JOIN test_table tb ON ids.id = tb.id AND tb.key = 'B' 
LEFT JOIN test_table tc ON ids.id = tc.id AND tc.key = 'C' 
LEFT JOIN test_table td ON ids.id = td.id AND td.key = 'D' 
LEFT JOIN test_table tc ON ids.id = te.id AND te.key = 'E'; 

在此查詢你得到所有的ID（如果你能柱回答「A」永遠在那裏你可以從那開始）。然後你必須加入給定ID的每個鍵。

如果你不能依賴於密鑰的數據類型，即A可以是字符串或日期，那麼你必須使用每個以下選擇：

COALESCE(ta.str_val,TO_CHAR(ta.date_val,'DD-MM-YYYY'),TO_CHAR(ta.num_val)) A, 
COALESCE(tb.str_val,TO_CHAR(tb.date_val,'DD-MM-YYYY'),TO_CHAR(tb.num_val)) B, 
... 
etc.