>>>Hi everybody, I want to begin developing a commercial application using VFP 9 as my front end and a free RDBMS (not DBFs) as the back end. I'd like to know what is the best one to work with VFP9. I have in mind 3: PostgreSQL, Firebird, and MySQL. I've never worked with them and of those three I guess MySQL is not completely free. I would like to know from the ones that have had any chance to work with any of those databases or perhaps any other that you may consider as a better alternative.
>>>
>>>TIA
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>>SQLExpress IMHO. This gives you most of the features of SQL Server (including reporting service) and direct scalability to huge databases. Free.
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>Thanks for the advice, but, I guess you have to pay for using Reporting service, right? I'm not sure about it.

The main problem will be if your application grows outside of the Express version capabilities (4GB of data and 1GB of RAM I think). At that point you will be tied up with SQL Server and you will have to pay to upgrade the version, that is the common trick these vendors do (Oracle does the same)

In my honest opinion with PostgreSQL or Firebird you will have no limitations from the beginning all for free.