After creating several diagram revisions you may need to compare two revisions of diagram or some diagram revision with it current version to examine what is changed. There is no separate tool for comparing diagram revisions in Database Designer for MySQL. But you can compare diagram revisions using Compare Diagrams tool easily.
This can be useful if you generated physical database from some diagram revision in the past. Then several changes were made to your diagram and you want to apply this changes to physical database. Database Modification will compare diagram with physical database, and this can lead to direct database changes to be lost (for example database was modified directly by other developer). If you generate SQL-code only for changes between revisions in your diagram you will not affect any other database objects besides changed in your diagram between this revisions.
To compare two diagram revisions or some diagram revision with its current version follow this steps:
1. Open diagram with revisions you want to compare.
2. Open Compare Diagrams tool using the Compare Diagram ( 
) item on Diagram tab of the Ribbon or press Ctrl + F6.
3. Currently opened model is selected by default at "Source (left) model" page. You need to select source diagram revision from Model Revision drop-down control. This is diagram revision you want to examine changes from. Then press Next button.
4. On "Target (right) model" page you need to select target diagram revision from the same drop-down control. This is diagram revision you want to compare source revision with. If you want compare source revision with current diagram version just left "HEAD revision" item selected in Model Revision drop-down control. Then press Next button.
5. Review selected diagram revisions at final wizard page and press Finish button.
6. Compare Result dialog will appear. Use "Show changes only" checkbox to hide unchanged items. There are all changes between selected revisions listed in this dialog.
7. Press Generate SQL button if you want to generate SQL-code to apply this changes to physical database. Or press Close button to close this dialog.
See also:
Diagram: Open an Existing Diagram
Diagram Functions: Compare Diagram | Diagram Versioning (Revisions) | Creating Diagram Revision | Revision Manager
Database Functions: Database Modification