TRUNCATE TABLE hr.emp;

  Truncate a table deletes all rows in a table and releases used space.

  Corresponding indexes are trunate.

The effects of using this command are as follows:

1、ALL rows in the table are deleted.

2、NO undo data is generated and the command commits implicitly because TRUNCATE TABLE is a DDL 

      command.

3、Correspondig indexes are also truncate.

4、A table that is being referenced by a foreign key cannot be truncated.

5、The delete triggers do not fire when this command is used.