顯示我收到的十個第一個聯繫人消息

Question

我想創建一個Sql語句，顯示我收到的十個第一個聯繫人以及他們最近發送的消息和時間。表列爲messageId, messageBody, fromUser, toUser, timeStamp，表格爲messages。數據庫是Mysql，Java是語言。但我希望這發生在一個單一的SQL語句。

Answer 1

我解釋「顯示十個第一接觸」，該提交的消息第一10人。

Select M2.fromUser 
    , LastMessage.messageBody 
    , LastMessage.timeStamp 
From (
     Select M1.fromUser 
      , Min(M1.timeStamp) As FirstMessage 
      , Max(M1.messageId) As LastMessageId 
     From messages As M1 
     Where M1.toUser = 'my username' 
     Group By M1.fromUser 
     Order By Min(M1.timeStamp) Asc 
     Limit 10 
     ) As M2 
    Join messages As LastMessage 
     On LastMessage.messageId = M2.LastMessageId 

Answer 2

SELECT fromUser, timeStamp, messageBody FROM messages ORDER BY timeStamp LIMIT 10 

Answer 3

您可以使用group by來查找每個聯繫人的最新消息。然後，你可以加入回消息表檢索郵件正文：

select LastTen.Contact 
,  LastTen.LastMessageDate 
,  msg.messageBody 
from (
     select fromUser as Contact 
     ,  max(timeStamp) as LastMessageDate 
     from YourTable 
     where toUser = 'YourName' 
     group by 
       fromUser 
     order by 
       max(timeStamp) desc 
     limit 10 
     ) LastTen 
join YourTable msg 
on  msg.fromUser = lastTen.Contact 
     msg.timeStamp = lastTen.LastMessageDate 

Answer 4

像這樣的東西可能會奏效：

SELECT fromUser, messageBody, timeStamp 
FROM (SELECT DISTINCT fromUser FROM messages ORDER BY timeStamp LIMIT 10) AS m1 
     LEFT JOIN messages 
     ON(fromUser) 
ORDER BY timeStamp DESC LIMIT 1