Oracle SQLPlus [Electronic resources] : The Definitive Guide, 2nd Edition نسخه متنی

Chapter 10. Exploring Your Database

You can create various objects in an Oracle database. You can create
tables, indexes on those tables, object types, constraints, and
various other objects. It's important to be able to
get information about the objects you have created. After a while you
are going to find yourself asking questions such as,
"What tables do I have defined?"
and "What do they look like?" You
may have an application fail because of a constraint violation. To
understand why the error occurred, you need to know what the
definition is for that constraint. Unless you have a good memory, you
will need to go to the database for this information.

Using SQL*Plus, you have two ways to display information about
objects within your database. The easiest way is to use the DESCRIBE
command. DESCRIBE will tell you about columns in a table or view.
DESCRIBE will also show you the definition of an object type or of a
PL/SQL package. The second method for getting information about
objects in your database is to query the Oracle data dictionary. The
data dictionary is a set of tables Oracle uses
to keep track of object definitions. To facilitate your use of the
data dictionary, Oracle provides a set of views known as
data dictionary views . This chapter shows you
how some of these views work and how you can write scripts to query
them.