Try this, Wayne:
USE Occupancy
;WITH BookingsToUpdate AS (
SELECT
*,
Seq = ROW_NUMBER() OVER (ORDER BY Booking_Skey)
FROM Bookings
)
SELECT
Seq,
Booking_Skey,
BookingNumber = 'B' + RIGHT('0000000' + CAST(Seq AS VARCHAR(8)),8),
AnotherBookingNumber = 'B' + RIGHT('0000000' + CAST(Booking_Skey AS VARCHAR(8)),8)
FROM BookingsToUpdate
For fast, accurate and documented assistance in answering your questions, please read this article.
Understanding and using APPLY, (I) and (II) Paul White
Hidden RBAR: Triangular Joins / The "Numbers" or "Tally" Table: What it is and how it replaces a loop Jeff Moden