CREATE TABLE blobtest (
blobval BLOB
);

INSERT INTO blobtest (blobval) VALUES ('abcde');

SELECT blobval
FROM blobtest;

SELECT DBMS_LOB.SUBSTR(blobval)
FROM blobtest;

UPDATE blobtest
SET blobval = EMPTY_BLOB();

SELECT DBMS_LOB.SUBSTR(blobval)
FROM blobtest;

UPDATE blobtest
SET blobval = NULL;

SELECT DBMS_LOB.SUBSTR(blobval)
FROM blobtest;

http://www.databasestar.com/oracle-empty_blob

A few examples of the EMPTY_BLOB function.

Oracle EMPTY_BLOB Function

sql, Oracle

SQL