This is the SQL Language forum. Questions about limits or capacities are always dependent upon the specific SQL implementation. In fact, I'm aware of no such numbers which are present in the SQL language specification (nor should there be).
For example, SqlMenace above cites limits particular to SQL Server. They may be quite different for, say, Oracle.
So, the question asked makes no sense unless it is relative to a specific SQL database implementation.
Jeff Mason
Custom Apps, Inc.
www.custom-apps.com