(Below datasets are made-up.) You have a file called Zip code mapping that you want to use to crosswalk zip codes and the corresponding county to another dataset that only has a field called "ZIP" containing zip codes but no fields containing county information. Below are sample records from the two files. Why might there be an error message when trying to do a crosswalk in SAS or in SQL, using ZIP_CODE_MAPPING.ZIP_CODE and PATIENT_ENCOUNTER.ZIP? Dataset #1: ZIP_CODE_MAPPING ZIP_CODE COUNTY 12345 NEW YORK 3478 RICHMOND 67800 QUEENS 83830 BRONX SEX Dataset #2: PATIENT_ENCOUNTER MRN ENCOUNTER_NUMBER 128830 12345678 324839 23456789 348494 34567890 ZIP 03478 F F 12345 67800 M