Access: Primary key fields formatted differently | forum

Hi

I recently attended an intermediate Access course on the 21 April 2016
The question I had which the trainer asked if i could submit via the forum was:
I quite often create reports from read only tables (I work in Bank) and the primary key is a 6 digit customer number. However, in some tables it is formatted as a number but in others to retain the leading zero it is formatted as text. This creates a problem and the way i get around it is to create a query of the text table and reformat the column as a number. ie CNUM: Format([KARTNR]*1,"000000")
This process seems to really slow down the running of the report - is there a better way to do this to improve effciency?
Thank you very much for your time
Nicholas Rowe