As others have said, you need proof.
I can hazard a guess as to the origins of this myth.
Sometimes the natural key to a table is composite, that is
1+ columns make of the primary key.
In that case, a number single column key will likely prove
faster, simply because there are fewer comparisons to make.
Though I don't know how much faster that might be. It may
be too small to measure without a large result set to test.
As an aside, Oracle recommends using SYS_GUID to generate
primary keys. Try this and see what data type you get:
SQL> select sys_guid() from dual;
Try using the dump() function, and look up the datatype code in
the datatypes section of the SQL manual.
Or just look at the docs for SYS_GUID.
Certifiable Oracle DBA and Part Time Perl Evangelist