樞轉在DB2

Question

我有我行轉成怎樣我的表結構從DB2 table.This列..

ItemID Item Value 
--------------------- 
1  Meeting  Now 
1  Advise  Yes 
1  NoAdvise No 
2  Meeting  Never 
2  Advise  No 
2  NoAdvise Null 
2  Combine Yes 

我想這被轉變爲（注意，我不想轉置合併）

ItemID Meeting Advise NoAdvise 
--------------------------------------- 
1   Now  Yes  No 
2   Never No  Null 

位掙扎着查詢，你能幫忙嗎？

Answer 1

這不是很漂亮，但它應該工作。 DB2沒有像SQL Server一樣的內置PIVOT函數。

​​3210

Answer 2

正如@bhamby所說的，DB2沒有PIVOT函數。
大多數情況下，我的查詢只是檢索結果的方式不同 - 您需要在其上運行profiler/optimizer以確保它正確，但我相信相關的子查詢可能會按行執行（可能效率較低），而不是集合。這不太可能是小數據集的問題。

WITH Item (id) as (SELECT DISTINCT itemId 
        FROM YourTable), 
SELECT item.id, Meeting.meeting, Advise.advise, NoAdvise.noadvise 
FROM Item 
LEFT JOIN (SELECT itemId, value as meeting 
      FROM YourTable 
      WHERE item = 'Meeting') as Meeting 
     ON Meeting.itemId = Item.id 
LEFT JOIN (SELECT itemId, value as advise 
      FROM YourTable 
      WHERE item = 'Advise') as Advise 
     ON Advise.itemId = Item.id 
LEFT JOIN (SELECT itemId, value as noadvise 
      FROM YourTable 
      WHERE item = 'NoAdvise') as NoAdvise 
     ON NoAdvise.itemId = Item.id 

（...其實，我有點擔心，你有兩個「勸」和「不提醒」，這似乎是某種形式的布爾條件列 - 也就是說，你應該有一個，但不是其他）。

Answer 3

的currently accepted answer by bhamby當然是正確的，但它是值得檢查if using several correlated subqueries is much slower than a single group by（提示：最有可能的是）：

SELECT 
    A.ItemID, 
    MAX(CASE WHEN A.Item = 'Meeting' THEN Value END) AS Meeting, 
    MAX(CASE WHEN A.Item = 'Advise' THEN Value END) AS Advise, 
    MAX(CASE WHEN A.Item = 'NoAdvise' THEN Value END) AS NoAdvise 
FROM A 
GROUP BY A.ItemID 

這也是在我看來有點簡單

SQLFiddle（在PostgreSQL的，但作品在DB2 LUW上）