Microsoft® SQL Server™ 2000 implements several built-in functions as user-defined functions that return a table. The invocation of these built-in user-defined functions follows special rules:
For built-in user-defined functions that return a table, the function name must be specified with a leading double colon (::) to distinguish it from user-defined functions that are not built-in. It also must be specified as a one-part name with no database or owner qualifications. For example:
SELECT *
FROM ::fn_helpcollations()
For built-in user-defined functions that return a scalar value, the function name must be specified as a one-part name (do not specify database or owner). Do not specify a leading double colon (::).