如何从mysql中的2个不同表中获取数据

Question

我有两张桌子：

Subscriber_detail

SubscriberID | Merchant_ID 
23           |  24

User_Detail

User_ID | User_RegisteredID

23      | 1001001
24      | 1001002

需要从User_RegisteredID

的User_Login表中提取SubscriberID and Merchant_ID from Subscriber_Detail

Answer 1

SELECT  sub.User_RegisteredID AS SubscriberRegisteredID,
        mer.User_RegisteredID AS MerchantRegisteredID
FROM    Subscriber_detail s
        JOIN User_Detail sub on s.SubscriberID = sub.User_ID
        JOIN User_Detail mer ON s.Merchant_ID = mer.User_ID

您需要加入两个表，并且User_Detail应该连接两次，因为表Subscriber_detail中有两列被引用。

如果一列 NULLABLE ，则应使用LEFT JOIN。

SELECT  sub.User_RegisteredID AS SubscriberRegisteredID,
        mer.User_RegisteredID AS MerchantRegisteredID
FROM    Subscriber_detail s
        LEFT JOIN User_Detail sub on s.SubscriberID = sub.User_ID
        LEFT JOIN User_Detail mer ON s.Merchant_ID = mer.User_ID