John, it has to be equal because it needs to be an exact match. Are you using a file connection, DB, or File Cabinet? The best way to do this would be to get an export not on the check infromation but on the invoice information. Hopefully the system you are getting this from would have the check number that paid that invoice. This way you have a list of invoices and then a column that would show what check paid that invoice. Then just do a match on invoice number and vendor number/name and pull in the check number from the column.
OR are you saying that is what you have but the invoice column has multiple values in it? If this is the case, not sure what you could do.. If they have commas or other separation values you could do some manipulation in excel..