Flagging a customer's second visit

Hi Ashish

Apologies - let me rephrase then as I do indeed want a calculated column formula, but not if it takes hours to calculate. (The model has now been running for 3 hours and is still not done). 

Is there an alternative to your suggestion above (either a calculated column, or a measure) that will be computationally efficient here? 

For example... first creating a calculated column in the CustomerMaster table (meaning one calc for each of 1mil customers, rather than one for each of 5-10mil transaction lines) that looks for the earliest transaction date of that customer after their very first transaction. Then the calculated column in the SalesRawData is just a simple lookup to the CustomerMaster table to see if the date matches.

If that concept makes sense (or any other ideas) I'll gather an extract of the appropriate data and post. Thank you!