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.