если не ошибаюсь, то для добавления строки с blob нужно сначала добавить строку с empty_blob, а потом сделать update

//вот пример из документации... 9.2.0

Example 1: Inserting a Word document into a BLOB Column using PL/SQL
The following code (steps 2-5) inserts MyResume.doc in the resume column of sam_emp table.

Create a directory object in Oracle. Here is how to create a directory object called MY_FILES which represents C:\MY_DATA directory.

You must have CREATE DIRECTORY privilege in Oracle.

create or replace directory MY_FILES as 'C:\MY_DATA';



Insert a row with empty BLOB in your table and return the locator.
Point to the Word file to be loaded from the directory created in Step 1, using the BFILE data type.
Open the file and use the locator from step 2 to insert the file.
Close the file and commit the transaction.

declare
f_lob bfile;
b_lob blob;

begin

insert into sam_emp(empno,ename,resume)
values ( 9001, 'Samir',empty_blob() )
return documents into b_lob;

f_lob := bfilename( 'MY_FILES', 'MyResume.doc' );
dbms_lob.fileopen(f_lob, dbms_lob.file_readonly);
dbms_lob.loadfromfile
( b_lob, f_lob, dbms_lob.getlength(f_lob) );
dbms_lob.fileclose(f_lob);

commit;

end;
/

из документации...

For a table on which you have defined a DML trigger, if you use OCI functions or DBMS_LOB routines to change the value of a LOB column or the LOB attribute of an object type column, Oracle does not fire the DML trigger.

а также...


Trigger Restrictions on LONG and LONG RAW Datatypes
LONG and LONG RAW datatypes in triggers are subject to the following restrictions:

A SQL statement within a trigger can insert data into a column of LONG or LONG RAW datatype.
If data from a LONG or LONG RAW column can be converted to a constrained datatype (such as CHAR and VARCHAR2), then a LONG or LONG RAW column can be referenced in a SQL statement within a trigger. The maximum length for these datatypes is 32000 bytes.
Variables cannot be declared using the LONG or LONG RAW datatypes.
:NEW and :PARENT cannot be used with LONG or LONG RAW columns.