| 34. 1. 2. Large Objects |
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Large objects (LOBs) may be used to store binary data, character data, and references to external files. |
LOBs are widely used to store documents such as Word and PDF documents. |
LOBs can store a maximum of 128 terabytes of data depending on the block size of your database. |
There are four LOB types: |
CLOB is the character LOB type. |
CLOB is used to store character data. |
NCLOB is the national language character LOB type. |
NCLOB is used to store multiple byte character data (typically used for non-English characters). |
BLOB is the binary LOB type. |
BLOB is used to store binary data. |
BFILE is the binary FILE type. |
BFILE is used to store pointers to files located in the file system. |
Columns created using CLOB and BLOB types have three advantages over those created using the older LONG and LONG RAW types: |
LOB columns can store up to 128 terabytes of data. |
This is far more data than you can store in a LONG and LONG RAW column. |
A LONG and LONG RAW column may only store up to 2 gigabytes of data. |
Note: The RAW type may store up to 4 kilobytes of data. |
A table can have multiple LOB columns, but a table can only have one LONG or LONG RAW column. |
LOB data can be accessed in random order. |
LONG and LONG RAW data can only be accessed in sequential order. |
A LOB consists of two parts: |
The LOB locator A pointer that specifies the location of the LOB content. |
The LOB content The actual character or byte data stored in the LOB. |
Depending on the size of the LOB content, the actual data will either be stored in the table or out of the table. |
If the LOB content is less than 4 kilobytes in size, the content is stored in the table containing the LOB column. |
If it's bigger, the content is stored outside the table. |
With BFILE columns, only the locator is stored in the database-the locator points to the external file containing the LOB content. |
Quote from: |
Oracle Database 10g SQL (Osborne ORACLE Press Series) (Paperback) |
# Paperback: 608 pages |
# Publisher: McGraw-Hill Osborne Media; 1st edition (February 20, 2004) |
# Language: English |
# ISBN-10: 0072229810 |
# ISBN-13: 978-0072229813 |