如何在同一个字段中查询2列？

Question

假设我有2个表：

USER(uid, uname);
ITEM(iid, description);
TRANSACTION(buyer, seller, item);

transaction.buyer和transaction.seller引用user.uid。 transaction.item引用item.iid

如何查询交易的买方和卖方的名称？

Answer 1

您需要两个联接：

select t.*, b.uname as buyerName, s.uname as sellerName
from transaction t join
     user b
     on t.buyer = b.uid join
     user s
     on t.seller = s.uid