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  Oracle Tips by Burleson

Large Objects (LOB)

People are putting more and more non-test stuff in their databases.  When they start placing pictures, video files, even their MS Word documents into the database, the database has to have a way to handle this unstructured data.  Enter the Large Object (LOB) data type.  A LOB stores unstructured data as an object.  It is stored offline, which means that a reference is stored in the table and the actual object is stored somewhere else.  This is important because a LOB can contain up to 4 Gigabytes of data.  Imagine searching a table with four LOB columns and a million rows if the LOBs were stored in the table columns!  LOBs come in 4 types.

CLOB  – Character LOB

BLOB  – Binary LOB

NCLOB  – National Language CLOB

BFILE  – File Stored outside the database on the server.

You manipulate LOBs using the dbms_lob package.

raw

A raw data type is data that is treated as binary data in that there is not manipulation by the database.  It is inserted as received and retrieved as is.  No character set conversion, etc.  A raw data type can be up to 2000 bytes in length.

longraw

Like the long data type, the longraw has been depreciated and should not be used.

rowid

A rowid  is a hexadecimal string representing the unique address of a row in its table.  You cannot store the logical rowid of an index-organized table.

urowid

Universal rowid.  Same as rowid except that it can store both physical and logical rowids, including those from an index-organized table.  Can also store a foreign table rowed, including those from remote non-oracle databases. 

So these are the Oracle basic data types.  Oracle allows you to create your own data types, but they must be constructed from the basic data types.  For example, if I wanted to have a column that contained the complete author address, I could create my own data type.  

CREATE OR REPLACE TYPE  full_mailing_address_type
AS OBJECT
( Street       VARCHAR2(80),
  City         VARCHAR2(80),
  State        CHAR(2),
  Zip          VARCHAR2(10) );
 

Here, I created a type called full_mailing_address_type.  I defined it using the Oracle built-in data types.  Once I have created this type in the database, I can use it in a table column.  This is called a user defined data type. 

CREATE TABLE customer
   (
     full_name            full_name_type,
     full_address         full_mailing_address_type,
   ); 

Here, I created a table with two columns, each containing a user defined data type.  The full_address column contains all the fields of my full_mailing_address_type data type.  User defined data types are a powerful feature but a bit advanced for this book, so we will confine our examples to the Oracle built-in data types. 


The above book excerpt is from:

Easy Oracle SQL

Get Started Fast writing SQL Reports with SQL*Plus

ISBN 0-9727513-7-8

Col. John Garmany 

http://www.rampant-books.com/book_2005_1_easy_sql.htm

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