What proportion of DBA skills are platform-independent?

I probably wouldn't go for this without further evidence of MySQL-specific knowledge or qualifications. You wouldn't hire an experienced Windows admin to take care of your Linux boxes either, would you? With experience in a different environment, you would know most of what to do, but probably not much about how to do it.

That said, MySQL offers a number of trainings and certifications, so maybe the candidate should take a round of those. That should get him up to speed with the product specifics.

It really depends upon the DBA.

I used to manage a few teams of them - Informix, Oracle, MS SQL and some are willing and eager to learn another platform, while others are not.

The basics are pretty much the same, but the details are very different.

I recently went back to hands on, in Oracle initially and had an opportunity to work on a SAP project using DB2. I had little DB2 experience before this, but with experience on many DB flavors came up to speed quickly.

You do not say which platform you are running MySQL on. If it is Windows, your friend would probably come up to speed very quicklky. A big part of being a DBA in a small shop is managing, tweaking, and tuning the host OS as well as the DB. If you are running it on Linux, I would have to ask how much xNIX experience he has as well as the DB experience.

I hope this helps.

Some skills are transferrable ie. database structure optimisation, sql, etc. as the same basic concepts apply to both MSSQL and MYSQL. However things like performance tuning and the way you go about task are highly specific to each platform.

I would say that it is possible to cross over with a little work as long as you have half decent Linux skills already.

But contrary to what someone said earlier I would take an MS DBA over a Linux admin if you can't get a Linux DBA because you can learn the Linux interfaces much more easily than DBA concepts and gotchas.