DBMS_LOB.substr() é a função certa a ser usada. Certifique-se de que haja dados na coluna.
Exemplo de uso:
-- create table
CREATE TABLE myTable (
id INTEGER PRIMARY KEY,
blob_column BLOB
);
-- insert couple of rows
insert into myTable values(1,utl_raw.cast_to_raw('a long data item here'));
insert into myTable values(2,null);
-- select rows
select id, blob_column from myTable;
ID BLOB_COLUMN
1 (BLOB)
2 null
-- select rows
select id, DBMS_LOB.substr(blob_column, 1000,1) from myTable;
ID DBMS_LOB.SUBSTR(BLOB_COLUMN,1000,1)
1 61206C6F6E672064617461206974656D2068657265
2 null
-- select rows
select id, UTL_RAW.CAST_TO_VARCHAR2(DBMS_LOB.substr(blob_column,1000,1)) from myTable;
ID UTL_RAW.CAST_TO_VARCHAR2(DBMS_LOB.SUBSTR(BLOB_COLUMN,1000,1))
1 a long data item here
2 null
