What can speed up a SQL count query?

Question

When doing a count (aggregate) SQL query, what can speed up the execution time in these 3 database systems? I'm sure many things could speed it up (hardware for one), but I'm just a novice DBA, so I'm sure I'll be getting a few answers here. I migrated about 157 million rows to a SQL Server database, and this query is taking forever. But in my source Netezza database, it takes seconds.

For example:

Netezza 6:

SELECT COUNT(*) FROM DATABASENAME..MYTABLE

Oracle 11g:

SELECT COUNT(*) FROM MYTABLE

SQL Server 2012:

SELECT COUNT(*) FROM DATABASENAME.[dbo].[MYTABLE]