Both SQL Server and Postgres allow indexes to be filtered by a condition.
Same behavior can be emulated in MySQL as described here: indexing - Workaround in mysql for partial Index or filtered Index? - Stack Overflow
I consider this to be an important addition, have had many use cases where a backend check needed to be applied instead of relying on DB checks, which are prone to user error and take longer to execute. DBDiagram has proven to be quite a useful tool and Iād be glad if they could support this feature as well.