sql查询联接条件与联接表

Question

我有这些下表：

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

地址表对我来说似乎不是问题，我使用此查询，对其进行了测试，并且工作正常。

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

现在问题出在phone_number表中，有2条记录和2个不同的条件，如您所见：

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

有phone_type字段-> phone和fax ，我想要显示两者的结果，如下所示：

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

我尝试以下查询：

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，该查询仅针对1个条件（ phone ），我如何获得传真值？

我使用PostgreSQL。

Answer 1

您可以使用不同的别名两次连接phone_numbers表，一次用于电话，一次用于传真。 如下面的P1（用于电话）和P2（用于传真）。

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')