Programming Microsoft Dynamics NAV - Fifth Edition

Field numbering

The number of each field within its parent table object is the unique identifier that NAV uses internally to identify that field. We can easily change a field number when we are initially defining a table layout, but after other objects, such as Pages, Reports, or Codeunits, reference the fields in a table, it becomes difficult to change the number of referenced fields. Deleting a field and reusing its field number for a different purpose is not a good idea and can easily lead to programming confusion.

We cannot safely change the definition of, re-number, or delete a field that has data present in the database. The same can be said for reducing the defined size of a field to less than the largest size of data already present ...