How to compare Blob datatype in a Trigger?

Question

Let's say I've the following trigger to log changes of "Document", which is in Blob type:
create or replace TRIGGER audit_file AFTER INSERT OR UPDATE OR DELETE ON MyFileTable FOR EACH ROW
BEGIN
BEGIN
IF updating('Document') AND(:OLD.Document != :NEW.Document) THEN
Log_This ('Document', :OLD.Document, :NEW.Document);
END IF;
end;
end;
Can ":OLD.Document != :NEW.Document" actually compare the content of those two docs, or do they just compare their locators/pointes? If yes, is there a built-in function I can use to do comparison of their actual content?

Answer 1

For BLOBs you can use
<p/>
  FUNCTION DBMS_LOB.compare(lob_1    IN BLOB,
                              lob_2    IN BLOB,
                              amount   IN INTEGER := 4294967295,
                              offset_1 IN INTEGER := 1,
                              offset_2 IN INTEGER := 1)
    RETURN INTEGER;