Now that you mention DB Designer (which is pretty nice) you should also look at DB Designer Fork which is (you guessed it) a fork of DB Designer that can generate SQL scripts for Oracle, SQL Server, MySQL and FireBird. In general this version is still very MySQL focused.

DB Designer is not developed anymore, but is succeeded by MySQL Workbench which keeps it focus on MySQL, but now there is both a FOSS and Commercial version.

I still prefer a more database agnostic software - therefore my preference for Power*Architect.

My experience in general regarding JDBC-drivers is that the client program must serve the correct data-type to the JDBC driver that matches the RDBMS data-types otherwise errors are likely to happen.

You can take a look at Kettle / Pentaho Data Integration. This is a very nice open source data integration/ETL (Extraction, Transformation and Loading) tool. It is more focused at integrating data from databases and other sources into data warehouse solutions, but it can also be used for "simple" excel transformations.

It is probably somewhat overkill for what you are after and it does have a learning barrier, but if you have some database knowledge it is very powerful.