PL/SQL DBMS_LOB.TRIM

Oracle’s DBMS_LOB.TRIM is a procedure provided by the Oracle Database within its Large Object (LOB) management functionality. This procedure is used to resize a LOB (Large Object) value by trimming it to a specified length. LOBs in Oracle can be used to store large amounts of data such as text, images, videos, and other multimedia formats directly inside the database. The DBMS_LOB package contains several procedures and functions to manipulate LOB data, and TRIM is one of them, specifically designed for adjusting the size of a LOB value.

Syntax

The basic syntax of the DBMS_LOB.TRIM procedure is as follows:

DBMS_LOB.TRIM(
   lob_loc   IN OUT NOCOPY CLOB | BLOB,
   newlen    IN     INTEGER);

lob_loc: This is the LOB locator that points to the LOB to be trimmed. It must be a locator for a BLOB (Binary Large Object) or CLOB (Character Large Object). The IN OUT NOCOPY mode means the LOB locator is passed by reference, and changes made by the procedure will affect the actual LOB value in the database.
newlen: This parameter specifies the new length for the LOB. The LOB will be trimmed or truncated to this length. If the newlen is smaller than the current size of the LOB, the data beyond newlen is lost. If newlen is larger than the current size of the LOB, an error is raised.

Usage

The DBMS_LOB.TRIM procedure is used when there is a need to reduce the size of a LOB value. This can be useful in various scenarios, such as when wanting to remove excess data from the end of a LOB or to free up space within the database. After trimming, the LOB will contain only the amount of data specified by the newlen parameter, starting from the beginning of the LOB.

Considerations

Permissions: To use DBMS_LOB.TRIM, you need appropriate privileges on the LOB or the table containing the LOB.

Transaction Boundaries: Operations performed by DBMS_LOB.TRIM are part of the transaction that encompasses the SQL statement calling the procedure. This means changes can be rolled back if not committed.

Temporary LOBs: DBMS_LOB.TRIM can also be applied to temporary LOBs, which are created and exist only for the duration of a session or transaction.

Example

Here is a simple example of how to use DBMS_LOB.TRIM:

DECLARE
   my_clob CLOB;
BEGIN
   -- Assume MY_CLOB is initialized and contains data
   -- Trim MY_CLOB to have a length of 10000 characters
   DBMS_LOB.TRIM(my_clob, 10000);
   
   -- Further processing can be done here
END;

This procedure is part of Oracle’s comprehensive support for managing large data within the database, providing developers and database administrators with tools to efficiently handle large volumes of data.