In the Alter Table dialog of MySQL Workbench:
- Go to Indexes tab.
- Double-click on a blank row to create a new index.
- Choose ‘UNIQUE’ as the index type.
- Check the columns that you want to be unique together.
There’s some discussion as to whether this is weird, since an index is not the same as a constraint. I certainly wouldn’t have thought to look there. However, apparently the `unique index’ enforces uniqueness in the same way as a unique constraint, and may improve performance. For example, if I try to insert a row that would break unique together after using this method, it throws an ‘1062 Duplicate entry’ error.