The licence terms are mostly dependent on the definition of "linking".  If  
your application links with MySQL code then it is required to be made  
available under the same terms.  The important libraries for linking with  
on Linux, such as glibc, are licensed under the LGPL rather than the GPL.

You are right though, it is in MySQL's interest to promote a very broad  
definition of "linking".  The MySQL JDBC connector used to be available  
under the LGPL but was changed to GPL a few years ago, presumably so that  
they could sell more commercial licences.

Beyond not distributing MySQL (and, more importantly, the JDBC driver)  
with your application, to be extra safe you should probably also ensure  
that your code makes no reference to anything MySQL-related (including  
JDBC URLs and driver strings).  If your application uses the standard JDBC  
API, and will work with other RDBMS options, then if one of your users  
downloads MySQL and its JDBC driver and configures your app to use it, I  
can't see how you can be held responsible for "linking".  Anything less  
clearly separated is a grey area.

Easiest solution: use PostgreSQL and avoid the hassle.  Oracle Express  
Edition (or the equivalent free version of SQL Server or DB2) might also  
be sufficient but it is a bit heavyweight.

Dan.

[me:]

Me, for one ;-)

I'll agree that there may be cases where an application is clearly independent
of MySQL, even if a MySQL installation is shipped with it, and the user is
given the option of installing it.  For the me (no lawyer) the criterion would
be "does the application clearly run, and do something useful (perhaps with
reduced functionality), if MySQL isn't available ?"  One easy way to achieve
that logical separation would be if the app worked just as well with a range of
DBMSs, and was capable of using whatever the user had installed (within
reason).  That doesn't seem too far away from the language of the GPL (section
2)

   These requirements apply to the modified work as a whole.
   If identifiable sections of that work are not derived from the
   Program, and can be reasonably considered independent
   and separate works in themselves, then this License, and
   its terms, do not apply to those sections when you distribute
   them as separate works. But when you distribute the same
   sections as part of a whole which is a work based on the
   Program, the distribution of the whole must be on the terms
   of this License, whose permissions for other licensees extend
   to the entire whole, and thus to each and every part regardless
   of who wrote it.

But I wouldn't want to bet money that a lawyer/court would agree that the
separation I mentioned above is sufficient to make the last quoted sentence
irrelevant.

And often, of course, applications do not have that degree of separation -- in
which case I would claim that the DBMS /is/ part of the delivered app and the
terms of the GPL apply in full force.

I'm not convinced that many people will pay much attention to how MySQL choose
to interpret the GPL.  Hell, I'm not convinced that many people even think
about how /they/ interpret the GPL beyond "I didn't pay for this stuff, so I
can do whatever I like with it".

But I do agree that it would be better if MySQL issued their stuff under a
licence which says what they want it to say, rather than (even partly)
overloading the GPL.

Agreed.

There's something to be said for that too.

   -- chris