Question

I’d like to know to which DBs can I connect, via DB Link, from a Microsoft SQL Server 2012 DB?

Is there a list?

Answer 1

I assume that by “DB link” you mean a “linked server”? There is no list, because as the documentation says:

SQL Server distributed queries are designed to work with any OLE DB
provider that implements the required OLE DB interfaces. However, SQL
Server has been tested against only the SQL Server Native Client OLE
DB Provider and certain other providers.

And:

OLE DB providers vary greatly in the type and number of parameters
required. For example some providers require you to provide a security
context for the connection using sp_addlinkedsrvlogin (Transact-SQL).
Some OLE DB providers allow SQL Server to update data on the OLE DB
source. Others provide only read-only data access. For information
about each OLE DB provider, consult documentation for that OLE DB
provider.

In other words, you can use any OLE DB provider to create a linked server but configuration and behaviour varies a lot.

MSDN includes a list of tested providers, although there is no SQL Server 2012 version of the page.