How to find new users

[#1]

I have a fact table which has a userid event date and an event time field. I need to determine when the user first appeared (became a new user) in the table. Then I will need to count new users in reports based upon various time slices

Anyone know the most efficient way to calculate the first date and time for the new user? Keep in mind that thefact table will be millions of rows. Thanks.

[Nicole-Smith]

FactTable:

LOAD *

FROM WhereEverYouHaveYourData;

LEFT JOIN (FactTable)

LOAD userid,

          min([userid event date]) as [first use date]

RESIDENT FactTable

GROUP BY userid;

Then you can use [first use date] as a filter (or hang a calendar off it it with month, year, or whatever time periods you're interested in).