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DROP/DELETE/TRUNCATE Tables

As we said at the beginning of the chapter, creating a table is DDL.  Dropping a table is also a DDL statement, because it modifies an object in the database rather that data in an object.

Each of these commands will either remove the table from the database or remove the rows from the table.  If we want to remove the table and all it’s data from the database, we use the drop command. 

SQL> drop table t1;
Table dropped.
 

The DROP  command is used to remove any database object from the database.  It works by removing the object definition.  Since the object no longer exists, it can no longer be used.  The drop command is DDL  because it defines objects in the database.  Anytime you execute a DDL command, you implicitly issue a commit and the statement cannot be rolled back.  This is discussed in the last section of this chapter.

The DELETE  command will not remove the table but will remove all the rows in the table.

SQL> select count(*) from t1; 
  COUNT(*)
----------
        10

1 row selected.

SQL> delete t1; 

10 rows deleted. 

SQL> rollback;

Rollback complete.

SQL> delete from t1; 

10 rows deleted. 

In this example, there are ten rows in table T1.  The DELETE T1 command deletes all ten rows.  The DELETE command is a DML command that does not issue an implicit commit.  For that reason, I can rollback the DELETE.  The DELETE FROM T1 command is the equivalent of the DELETE T1 command and can also be rolled back.  We will cover deleting rows in detail later.  The rollback command will be covered in the last section of this chapter.


The above text is an excerpt from:

Easy Oracle SQL
Get Started Fast Writing SQL Reports with SQL*Plus

ISBN 0-9727513-7-8

by John Garmany
 


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