Difference between TRUNCATE, DELETE and DROP commands

DELETE

The DELETE command is used to remove rows from a table. A WHERE clause can be used to only remove some rows. If no WHERE condition is specified, all rows will be removed. After performing a DELETE operation you need to COMMIT or ROLLBACK the transaction to make the change permanent or to undo it. Note that this operation will cause all DELETE triggers on the table to fire.

 DELETE FROM emp;

TRUNCATE

TRUNCATE removes all rows from a table. The operation cannot be rolled back and no triggers will be fired. As such, TRUCATE is faster and doesn't use as much undo space as a DELETE.Truncate is also delete the records but it is not delete the table space which is created by the data base.

TRUNCATE TABLE emp;

DROP

The DROP command removes a table from the database. All the tables' rows, indexes and privileges will also be removed. No DML triggers will be fired. The operation cannot be rolled back.We can not recover the table before Oracle 10g. But Oracle 10g provide the command to recover it by using the command (FLASHBACK)
Drop command will delete the entire row also the structure.But truncate will delete the contenets only not the strucure, so no need to give specifications for another table creation.

 DROP TABLE emp;