Not sure I fully understand, but you could probably try joining them. Any chance you could share an anonymized sample of your data so we can get a better idea of what you're trying to do?
Yes I can join them but after the join I would like to tag or mark up on the large data set where the unique booking number appears in both data sets so I can then isolate the unique booking numbers which feature across both data sets. Does that make sense?
Not sure if I can share the data sets very easily Sorry