it depends on how the database application changes the files. If it simply adds the data to the end of the file, only the new data has to be uploaded. If the data is added within the file, the new data and all old data afterwards have to be reuploaded.
Generally, BoxCryptor encrypts blocks of data (normal block size is 4 KB) and the number of a block is taken into account when encrypting a block (so a block is encrypted differently depending on its position within a file). When a file is changed there are 3 scenarios:
a) Parts of a file are changed but the file size is exactly the same: Only the changed blocks have to be reencrypted and reuploaded.
b) Parts of a file are changed and the file size is changed: The changed blocks and all following blocks have to be reencrypted and reuploaded. (e.g. if data is inserted within the file)
c) Data is added/deleted from the end of a file: Only the added data has to be uploaded
Hope I could help you,