Databases Reference
In-Depth Information
This output shows that the table
DOMAIN_NAMES
has three objects that are dependent on it: a function, a trigger,
and a synonym.
the DUaL taBLe
the
DUAL
table is part of the data dictionary. this table contains one row and one column and is useful when you
want to return a row and you don't have to retrieve data from a particular table. in other words, you just want to
return a value. For example, you can perform arithmetic operations, as follows:
SQL>select 34*.15 from dual;
34*.15
----------
5.1
other common uses are selecting from
DUAL
to show the current date or to display some text within an
sQl script.
Summary
Sometimes, you're handed an old database that has been running for years, and it's up to you to manage and maintain
it. In some scenarios, you aren't given any documentation regarding the users and objects in the database. Even if you
have documentation, it may not be accurate or up-to-date. In these situations, the data dictionary quickly becomes
your source of documentation. You can use it to extract user information, the physical structure of the database,
security information, objects and owners, currently connected users, and so on.
Oracle provides static and dynamic views in the data dictionary. The static views contain information about the
objects in the database. The dynamic performance views offer a real-time window into events currently transacting in
the database. These views provide information about currently connected users, SQL executing, where resources are
being consumed, and so on. DBAs use these views extensively to monitor and troubleshoot performance issues.
The book now turns its attention toward specialized Oracle features, such as large objects, partitioning, Data
Pump, and external tables. These topics are covered in the next several chapters.
