Crystal Record Selection Formula - Distinct Values?

[Jasper Jones]

I have a Crystal report that shows me a list of sales and which
customer bought them, I would like to get a distinct list of
customers, is this possible with crystal's formulas?

This is my query:

crReportDocument.RecordSelectionFormula = "{sales.city} = 'London')"
It produces records like this

NAME City
Bobby Joe London
John Smith London
Bobby Joe London
Bobby Joe London
Bobby Joe London
Gordon Banks London

I really want to just show a distinct list from the CITY coloum so I
get this instead:

NAME City
Bobby Joe London
John Smith London
Gordon Banks London
Can some body help me with this? I tried a few variations with the word
distinct in the Record Selection Formula but I haven't had any luck.