聯接表而不刪除行

Question

我有一個表（地址），如下所述：

我想為每個用戶選擇所有數據作為一行。 我嘗試了左連接，效果很好。 例如

select A.Address as permaddress, B.Address as mailaddress from Addresses A left join  Addresses B on A.userId = B.userId and B.address_type = 'mail' where A.address_type = 'perm' and A.userId = '987654321'.

當我將其擴展到2個具有address_type ='camp'的左連接時，它不起作用。 例如

select A.Address as permaddress, B.Address as mailaddress, C.Address as campaddress from Addresses A left join  Addresses B on A.userId = B.userId and B.address_type = 'mail'
left join Addresses C on A.userId = C.userId and C.address_type = 'camp'
 where A.address_type = 'perm' and A.userId = '987654321'.

我不想做一個簡單的聯接，因為如果某人沒有其他address_types，它將刪除行。 問題是每個人都有address_type ='perm'。 例如：

select A.Address as permaddress, B.Address as mailaddress from Addresses A, Addresses B  where A.userId = B.userId and B.address_type = 'mail' and A.address_type = 'perm' and A.userId = '987654321'.

不知道是否應該讓我不參加相同的表，還是應該只使用代碼選擇幾次。 例如

select A.Address as permaddress from  from Addresses A where A.address_type = 'perm' and A.userId = '987654321'

然后做

select B.Address as mailaddress from  from Addresses B where B.address_type = 'mail' and B.userId = '987654321'

然后使用代碼合並結果

任何幫助將不勝感激。 謝謝。

Answer 1

使用左聯接時，將顯示所有結果，無論它們是否具有mailaddress或campaddress的值。

select    A.Address as permaddress, B.Address as mailaddress, C.Address as campaddress
from      Addresses A 
left join Addresses B on A.userId = B.userId and B.address_type = 'mail' 
left join Addresses C on A.userId = C.userId and C.address_type = 'camp' 

where     A.address_type = 'perm' 
  and     A.userId = '987654321'

Answer 2

您可以使用PIVOT實現此目的。

不習慣Oracle語法，但這應該可以解決問題。

SELECT *
FROM   (SELECT userid, address_type, address from Addresses)
PIVOT  (MAX(address) AS address FOR (address_type) IN ('perm', 'mail', 'camp'));

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