If you're worried about the future, Oracle agreed to maintain the dual-licensing strategy until at least 2015 as part of the EU negotiations before acquiring Sun.
The FSF call it "mere aggregation": http://www.gnu.org/licenses/gpl-faq.html#MereAggregation
I don't know whether SUN and Oracle still pursue that strategy. Otherwise you could indeed bundle MySQL with some clean-room libraries to talk to the server.
That doesn't sound legal. You're allowed to clean-room implement anything aren't you?
That does indeed sound crazy, but they also had piles of cash to throw at lawyers to go after anyone who challenged them, and (maybe as a result of that) nobody ever made e.g. a clean-room BSD or LGPL licensed version of the mysql library. So it never made it to court AFAIK.
The reality is that copyright covers verbatim copying. If you read a book and write a review, the term "derived work" makes English sense, but not legal sense. Similarly, if you read the MySQL code looking for magic words to say to the server to get it to give you data, saying those words is not copyright infringement. It's "learning", not "copying".
If anyone used MySQL, I would write a BSD-licensed API just to prove a point. (And to be non-blocking.) But the world has moved on since the Oracle deal...
What would happen, if the protocol would require sending a picture of a picture of Mickey Mouse with each request (or some copy-righted novel)?
In fact if you spend much time thinking about this it isn't at all hard to come up with a lot of scenarios that law doesn't have an answer for, in theory or in practice.
In short, it's fair use.
I believe MySQL/Sun used to make a lot of money dual licensing the GPL client library. No longer!
It doesn't. The acceptance of the GPL (as of V2, haven't read V3) for a software component does not compel you to use any particular license for your own work. You can, by distributing the GPL'd work with you own non-open software, be in violation of the license on the GPL'd work, but the repercussion is a loss of the right to distribute the GPL'd work potentially enforced by injunction, and not an automatic change of your own license as the phrase "make your application GPL as well" implies.
If you are redistributing it (you ship it to your customers and they deploy it on their servers) I would find a lawyer.
I also wonder how these pricing changes impact the already hurting community of open source developers supporting the community version.
It's clear that someone doing proprietary software on top of mysql have to get proprietary-compatible license for mysql.
But. How this happens, that community submitted code/patches/etc gives Oracle profits? Isn't including any patch/code from GPL version into Proprietary version automatically enforce GPL rules and makes impossible to include this software into any other proprietary software?
I saw this with other projects too. I am really interested how company behind product can provide both proprietary and gpl licenses for their products.