您在这里有几个选项，但使用添加一个 ROW_NUMBER 按 user 分组并排序(降序)于您的 时间戳 可让您轻松选择最新记录.

You have several options here but using adding a ROW_NUMBER grouped by user and sorted (descending) on your timestamp allows you to easily select the latest records.

使用 ROW_NUMBER

SELECT *
FROM   (
         SELECT ID, voting_ID, username, timestamp, XMLBallot
                , rn = ROW_NUMBER() OVER (PARTITION BY voting_ID, username ORDER BY timestamp DESC)
         FROM   Ballots
       ) bt 
WHERE  rn = 1

或者，您可以选择每个用户的最大时间戳并加入.

Alternatively, you can select the maximum timestamp per user and join on that.

使用 MAX

SELECT bt.ID, bt.voting_ID, bt.username, bt.timestamp, bt.XMLBallot
FROM   Ballots bt
       INNER JOIN (
          SELECT username, voting_ID, timestamp = MAX(timestamp)
          FROM   Ballots
          GROUP BY
                 username, voting_ID
        ) btm ON btm.username = bt.Username
                 AND btm.voting_ID = bt.voting_ID
                 AND btm.timestamp = bt.timestamp