Using CLOBs and BLOBs : Introduction « Large Objects « Oracle PL/SQL Tutorial

LOB columns store a locator that points to the LOB contents.

Initializing a CLOB and BLOB

Before you can actually write content to a LOB, you must first initialize the LOB column.

You do this by calling an Oracle database function that generates and returns a value for the locator.

To initialize a CLOB or NCLOB column, you use the EMPTY_CLOB() function.

A BLOB column must be initialized using the EMPTY_BLOB() function.