Question

As far as I know, BOL exmaple on fn_trace_getinfo used to use
:: instead of sys schema in the example like following

From

    SELECT * FROM ::fn_trace_getinfo(default)

To

    SELECT * FROM sys.fn_trace_getinfo(default)

Are there any differences between those two?
And what does :: mean?

Answer 1

OK, i hope this (UDF starting with fn_…) helps

From the page it seems that :: would tell Sql Server that this has to be a System UDF, and will only be found in Master DB.

Q:

I’ve read frequently how stored
procedures we create shouldn’t be
named with sp_ since SQL Server will
first check the master db before the
current db when trying to find the sp
to execute. I always nodded and
thought how I was glad I hadn’t done
that. For some reason it never clicked
that UDF behavior could be the same.

I have several UDFs that start fn_…
When I reference a UDF as dbo.fn_…
does SQL Server check the master db
for these and only upon not finding
them check the current db? If so, is
there a performance hit for this?

A:

No. To call a system-supplied UDF, you
need to use ::, so that is what SQL
Server looks for. All system-supplied
UDFs are table functions, as scalar
system functions are not UDFs at all.