query last n hours / minutes

I have an Oracle 9 table with a field performed_date.

Select * from my_table
where performed_date > (sysdate - 8);

This will return all records with performed_date within last week.

What is the query for "last 4 hours"?

What is the query for "last 30 minutes"?

TIA Received on Fri Jul 29 2005 - 00:24:11 CDT