merge data

I have been asked to develop a project with 7 columns and an import function. The user will have 2 files. One has only 2 columns, being sheet number and description. The second file has the same columns as the first file plus 5 extra columns. The file with the extra columns have matching sheet numbers but the description column has no data. The idea is to import the file with the 7 columns first then import the file with just the 2 columns. The empty descriptions would them populate based on the common sheet numbers. Any ideas on how to go about this? Thanks in advance.