Select newest datetime for each userid MS Sql Server

I have a table used for a chat. Among others there is a field called userid and a field called timesent. I need to know the latest timesent for each userid in the table, so that I can delete them from the table if they haven't said anything for 3 minutes, in which case I will assume they are gone.

I can't really crack this nut... How do I query.

I could of course split it up and first select all the userids and then loop through them and select top 1 timesent in my method, but I was wondering if sql alon开发者_运维百科e can do the trick, so I don't need to execute tons of queries.

To get the latest timesent per userid you can use MAX

SELECT userid, MAX(timesent) AS timesent
FROM your_table
GROUP BY userid

Or to do the specified delete you can use

DELETE your_table 
FROM   your_table y1 
WHERE  NOT EXISTS(SELECT * 
                  FROM   your_table y2 
                  WHERE  y2.userid = y1.userid 
                         AND y2.timesent >= DATEADD(MINUTE, -3, GETDATE()))