Microsoft definitely does not have a version of SQL Server for Macs. They would have to rewrite the entire product in order to do that. The fact that they also own Windows makes them reluctant release their products for other operating systems.
Really, the only significant software they release for Macs is Microsoft Office. I'm guessing they do that because it is very profitable for them and keeps people from migrating to some other office software. I imagine that they probably would release SQL Server for Macs if there was strong demand for it, but that demand simply isn't there.