Changes to Fields
During a download if a change is detected to a Salesforce field datatype and that same change can be made to the SQL object table without risk of losing data then the field datatype will be updated on SQL.
If the datatype change could result in data loss, then the field will be excluded from the object download. All other fields on the object will continue to be downloaded.
Changes that can be made are normally those that increase the range of the datatype. For example increasing the scale on a numeric field or the length on a text field. Changes such as reducing field size or converting between base types – such as numeric to text cannot be made.
You can report on any fields that have been excluded from downloads due to datatype changes with the following query.
select * from sfm.sfm_fields_history_v where action_code = 'Download' and task_name = 'Update Field Download Status'