[ Just a repeat, but useful for upstreams and downstreams and people building modern apps using MySQL’s connector libraries and other components that need GPLv3 ] Via David Ayers, I read that the GPLv3 has been added to the FOSS License Exception on the MySQL website (disregard the "Updated" date at the top of that page, this is fairly recent). This means that the GPLv2 licensed library may be combined with GPLv3 code, leaving the combined work as a whole under the terms of the GPLv3, while only the terms of the GPLv2 apply to the client libraries.
Some things to note if you read that exception page closely: "GPL" there means "GPLv2" except in the table of FOSS licenses, where it means GPLv3. Clause 2b means "this exception applies if no other part of the work forces you to use GPLv2". Clause 2d adds additional source distribution requirements beyond what you’d have to do otherwise. The page also still refers to Sun, so it needs another update anyway, one which might get a good going-over by Oracle’s lawyers.