[SOLVED] MySQL query - find "new" users per day

MySQL query - find "new" users per day

I have a table of data with the following fields

EventID        : Int, AutoIncrement, Primary Key
EventType      : Int                             ' Defines what happened
EventTimeStamp : DateTime                        ' When the Event Happened
UserID         : Int                             ' Unique

The query needs to tell me how many events occurred with new UserIDs for each day in the whole set. So, for each day, how many events exist which have a UserID which doesn't exist in any prior day. I've tried lots, and I can get unique users per day, but can't work out how to get 'NEW' users per day.

Solution

Thank you all for your help - I've voted up the assistance. Here's what I did:

I created these 2 views (I needed to end up with a view, and had to create 2 as it seems you can't nest select statements within views).

Sightings:

select min(to_days(`Events`.TimeStamp)) AS Day0,
    `Events`.TimeStamp AS TimeStamp,
    `Events`.UserID AS UserID
from `Events` group by `Events`.UserID order by `Events`.UserID

NewUsers:

select count(distinct Sightings.UserID) AS Count,
    date(Sightings.TimeStamp) AS Date from Sightings
    group by date(Sightings.TimeStamp)