Question

我的留言表包含两个字段senderid和recipientid。我需要列出所有邮件，但senderid和recipientid中的值组合不需要重复。

例如，如果senderid = 4和recipientid = 2，我只需要一个组合值;要么是4,2，要么是2,4。

任何人都可以帮我这么做吗？

提前致谢;）

Answer 1

select
    message,
    case when senderid < recipientid then recipientid else senderid end,
    case when senderid < recipientid then senderid else recipientid end
from m
group by
    message,
    case when senderid < recipientid then recipientid else senderid end,
    case when senderid < recipientid then senderid else recipientid end

Answer 2

select *
from myTable a
where not exists
(
    select top 1 1 
    from myTable b
    where a.senderId = b.receiverId
    and a.receiverId = b.senderId
    and a.senderId < b.senderId
)

Answer 3

想法很简单，只需确保发件人/收件人ID的连接方式使得较小的ID位于较大的ID前面。

select
  pair, count(*) 
from 
  (select if(senderid<recipientid, concat(senderid, ',', recipientid), concat(recipientid,',',senderid)) as pair from messages) pairs
group by pair;

注意这种选择的表现。也许你想在插入记录时创建一个额外的列来存储对值，并将列编入索引。

sql查询组由特定结果作为两个字段值的组合值

3 个答案: