Coding in mysql is very different from either Oracle or SQL server especially as you get to the more complex database postions such as business information jobs or data analyst jobs. However, it is better experience than no database experience at all. If I were to put that in a job advertisement, I would consider that people with actual experience in the database I wanted would be at the top of my list and people with experience in some other database would be in the next tier unless they had domain experience or had done something extraordinary. And based on what I know about databases I would be inclined to prefer Oracle candidates over MySQl candidates if I had no great SQl Server candidates.
So suppose I was looking for a data analyst for a financial services company dealing with terrabyte-sized databases.
My first pick to interview would be a sql server person with experince in the financial sector and experience in large databases.
My next pick might be an Oracle person with experience in large databases and the financial sector.
My third pick might be a SQL Server person with experience in some other business sector and experience with large databases.
My fourth pick might be a person who had extensive MySQl experience in the financial sector but not dealing with datbases as large as ours.
My fifth pick might be a SQL Server person with no financial experience and no large database experience.
Other people might rank them differntly depending on how important the skill was and what other achievements the applicant had. I tend to discount resumes that only talk about responsibilities for instance. I want people who think in terms of accomplishments. That might be enough for me to give the edge to someone who doesn't have the exact skill set I am looking for over someone who does, but doesn't appear to have done anything interesting with it.
Now if the job was not mostly a database job, it would be much easier to get into the interview pile because other skills such as C# or Java might be a much greater portion of the job and the actual level of database skill needed might be at a lowere level and easier to pick up.
However since you never know the skills of the other people who apply or exactly how each hiring official will rank them, it is worth a shot at applying if you think you can do the job. Just don't think you will automatically get an interview.
However, if you want to get into real database programming (as opposed to it being a side duty of application programming) then you need to get some SQL Server or Oracle experience. In that case, download the free versions and start learning the syntax differnces or invest in the developer edition of SQL server and learn SSIS.