比较同一表中两列中的值并创建新列

Question

这一定很容易查询，但由于某种原因，我无法获得正确的查询。 我正在使用 Oracle SQL。 我有一张桌子，上面有互相送礼物的人的详细信息，我想跟踪互相交换礼物的人。 我正在尝试比较同一张表中的两列。

桌子：

SenderId  |  Sender    |  ReceiverId  |  Receiver  |
   1      |  Christen  |       30     |  Sharyn    |
   2      |  Will      |      5       |  Madeline  |
   7      |  Kim       |      25      |  Lee       |
  30      |  Sharyn    |       1      |  Christen  |
  25      |  Lee       |      7       |   Kim      | 

预期结果表：

 Sender    |  Receiver  | Exchanged_Gift
 Christen  |  Sharyn    |      1
 Will      |  Madeline  |      0
 Kim       |  Lee       |      1

由于有两组人交换了礼物，如果他们交换了礼物，则新列将有1，否则为0。

第一组——克里斯汀和莎琳都交换了礼物。
第二组——金和李也交换了礼物。

Answer 1

您可以简单地使用least和greatest function 如下：

Select case when count(1) = 1 then max(sender) else least(sender,receiver) end as sender, 
       case when count(1) = 1 then max(receiver) else greatest(sender,receiver) end as receiver,
       count(1) - 1 as exchanged_gifts
  From your_table
Group by least(sender,receiver), greatest(sender,receiver)

Answer 2

这有点棘手，因为当只有一行时，你想保持原来的顺序。 一种方法是使用union all进行聚合：

select least(sender, receiver) as sender, greatest(sender, receiver) as receiver, 1 as exchanged
from t
group by least(sender, receiver), greatest(sender, receiver)
having count(*) = 2
union all
select sender, receiver, 0
from t
where not exists (select 1
                  from t t2
                  where t2.receiver = t.sender and t2.sender = t2.receiver
                 );