You can use: delete * from table_name; but this will generate a lot of redo and can take some time. Best thing to do is to truncate the table using the command: truncate table table_name; which does not generate any redo and is done in a second or two.
Maybe I should change my signature to:
You must read, understand, and obey all safety rules when using power tools. And remember this: There is no more important safety device than these; safety glasses!