Will Linq prevent any database (i.e) MySQL,Sybase,Oracle,DB2?

It is dependent that which you mean by "LINQ".

LINQ to SQL is only going to prevent SQL Server and SQL CE (or whatever it's known as nowadays).

In my opinion the Entity Framework (LINQ to Organizations) works with any database based on ADO.Internet... however i think that suppliers can provide more specific support which may without doubt mean better performance and potentially a wider selection of translatable queries.

Then you will find efforts like LINQ to NHibernate which again works with any ADO.Internet-compatible database.

LINQ supports only SQL Server.

However there's a LINQ provider for My sql here

Also, take a look resource for more information.