sql查詢與條件上加入連接表

Question

我有這些下表：

suppliers

id | name 
----------- 
1 | sample 

addresses

id | address | owner_type | owner_id 
------------------------------------- 
1 | adres | Supplier | 1 

phone_numbers

id | number | owner_type | owner_id | phone_type 
------------------------------------------------ 
1 | 12345 | Supplier | 1  | phone 
2 | 67890 | Supplier | 1  | fax 

對地址表來說，這似乎不是一個問題，我使用這個查詢，我測試了它，它工作正常。

Select suppliers.*, addresses.address AS address FROM suppliers LEFT JOIN addresses ON (addresses.owner_id = suppliers.id AND addresses.owner_type = 'Supplier') 

現在的問題是在phone_number表中，有2條與2個不同的條件，你可以看到：

id | number | owner_type | owner_id | phone_type 
------------------------------------------------ 
1 | 12345 | Supplier | 1  | phone 
2 | 67890 | Supplier | 1  | fax 

有phone_type場 - >phone和fax，我想在結果表明兩者的是，像這樣的：

id | name | address | phone | fax 
--------------------------------- 
1 | sample | adres | 12345 | 67890 

我嘗試此查詢：

LEFT JOIN phone_numbers ON (phone_numbers.owner_id = suppliers.id AND phone_numbers.owner_type = 'Supplier' AND phone_type = 'phone') 

不幸的是，查詢只適用於1條件（phone），我如何獲得傳真值？

我使用PostgreSQL。

Answer 1

您可以使用不同的別名將phone_numbers表加入兩次，一個用於電話，一個用於傳真。如P1下面的電話和P2的傳真。

Select suppliers.*, addresses.address AS address ,P1.number as 'Phone', P2.number as 'Fax' 
FROM suppliers 
LEFT JOIN addresses ON (addresses.owner_id = suppliers.id AND addresses.owner_type = 'Supplier') 
LEFT JOIN phone_numbers P1 ON (P1.owner_id = suppliers.id AND P1.owner_type = 'Supplier' AND P1.phone_type = 'phone') 
LEFT JOIN phone_numbers P2 ON (P2.owner_id = suppliers.id AND P2.owner_type = 'Supplier' AND P2.phone_type = 'fax')