Tables :: Combining Two Text Columns Into One In A Table?

My Approach database contains records relating to nearly 800 sites in London. There are radically different amounts of data held about each site. The database contains a lot of different tables, each containing a different class of information. Not all the sites listed in the database have information in all of the tables.

The unique thing that holds it all together is the unique site reference number. Unfortunately this is split into two separate columns in the Approach database, "Reference" and "Suffix". Not all sites have a suffix. (The purpose of the suffix is to identify sub-sites which are subordinate to the main site reference, but need to have their own individual records.) Because many sites have no suffix, most of the fields in the second column are blank.

In order to link all the tables together in access I need a Primary Key which is unique to each site. In this case the reference/suffix number is the obvious (only) candidate. There is no problem using two different columns to create a primary key. The problem I face is that it doesn't like the fact many of the fields in the second column are blank.

My solution to this is to combine the two columns into one. That would give every site a unique reference, and none of the fields in the combined column would be blank. Can I work out how to do it? All I want is a new column that displays the reference and suffix (if any) in a single field, no spaces.