CLOB Data type

You can use the CLOB data type to store a block of text. It is designed to store ASCII text data, including formatted text such as HTML or PostScript. Although you can store any data in a CLOB object, IBM Informix tools expect a CLOB object to be printable, so restrict this data type to printable ASCII text.

CLOB values are not stored with the rows of which they are a part. They are allocated in whole disk pages, usually areas away from rows. (For more information, see your IBM Informix: Administrator's Guide.)

The CLOB data type is similar to the TEXT data type except that the CLOB data type provides the following advantages:

• An application program can read from or write to any portion of the CLOB object.
• Access times can be significantly faster because an application program can access any portion of a CLOB object.
• Default characteristics are relatively easy to override. Database administrators can override default characteristics for sbspace at the column level. Application programmers can override some default characteristics for the column when they create a CLOB object.
• You can use the equals operator (=) to test whether two CLOB values are equal.
• A CLOB object is recoverable in the event of a system failure and obeys transaction isolation modes when the DBA or application programmer specifies it. (Recovery of CLOB objects requires that your database system has the necessary resources to provide buffers large enough to handle CLOB objects.)
• You can use the CLOB data type to provide large storage for a user-defined data type.
• DataBlade developers can create indexes on CLOB data types.

The disadvantages of the CLOB data type are as follows:

• It is allocated in whole disk pages, so a short item wastes space.
• Restrictions apply on how you can use a CLOB column in an SQL statement. (See Using Smart Large Objects.)
• It is not available with all Informix database servers.