Question

I’ve got a game which dumps state information to a database. Eg. Connected, Lost Connection, Grabbed Screen Dump, etc.

Each state is defined by a field called StateTypeId, which is a foreign key to a simple lookup table 'StateTypes'.

Now, i’m trying to find all the people who are currently ‘Connected‘ (eg. StateTypeId == 1), and i’m not sure how to do it. When i say currently connected, I mean that a user doesn’t have a ‘LostConnection‘ state (ie. StateType == 2) as their most recent entry.

I was thinking along the lines of.

SELECT UserId FROM UserData WHERE StateType = 1 GROUP BY UserId 

or

SELECT UserId FROM UserData WHERE StateType != 1 GROUP BY UserId 

but this returns all the results, not just the most recent stuff.

Any suggestions?

(i’m guessing I’m missing a TOP(1) and some rank/order by stuff?)

EDIT

DOH! i forgot to mention, i DO have a DateTime column in the table -> DateEntered.

EDIT 2 – Clarification of question AND some sample data.

I’ve tried the suggested solutions and i’m not having much luck. As such, i’ll provide some sample data to see if this helps clarify my question.

ID State          UserName DateAdded 1  Connected      Foo      1/1/2000 12:00  2  Connected      Bar      1/1/2000 12:01   3  ScreenShot     Foo      1/1/2000 12:05  4  LostConnection Foo      1/1/2000 12:06 5  Connected      Joe      1/1/2000 12:10 6  LostConnection Joe      1/1/2000 12:15 7  Screenshot     Bar      1/1/2000 12:16 8  Connected      Jane     1/1/2000 12:22 

So looking at this, the people who are connected (currently) are Bar and Jane. Foo and Joe are gone. Also note, Bar’s last activity a screenshot, meaning, his last activity was not a LostConnection state.

HTH.

Answer 1

What you are looking for is the ‘most recent’ entry having a StateType of 1 or 2:

Then you are looking to identify the ‘last’ one for each user:

select UserName, max(DateAdded) as LastDate from UserData where State IN ('Connected', 'LostConnection') Group by UserName 

Then you need to check the state of these (which requires a join with the original table):

SELECT UserName FROM UserData allData join      (select UserName, max(DateAdded) as LastDate     from UserData     where State IN ('Connected', 'LostConnection')     Group by UserName) as lastData on allData.UserName = lastData.UserName         and allData.DateAdded = lastData.LastDate WHERE StateType = 'Connected' 

Another way to join would use the id of the UserData like this:

SELECT UserName FROM UserData allData join      (select max(id) as id -- if ids are assigned in ascending order     from UserData     where State IN ('Connected', 'LostConnection')     Group by UserName) as lastData on allData.id = lastData.id WHERE StateType = 'Connected'