• 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

    “Write the query the simplest way. If through testing it becomes clear that the performance is inadequate, consider alternative query forms.” - Gail Shaw

    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