ORA-00932: inconsistent datatypes: expected - got BLOB

I have written this SQL but am getting the following error:

ORA-00932: inconsistent datatypes: expected - got BLOB

Here is SQL :

SELECT DISTINCT
    file_name,
    JPEG_IMG 
FROM
    table_repo
WHERE
    file_name = 'K1A98'
    AND JPEG_IMG IS NOT NULL; 

It would have helped if you posted test case.

Sample table: note that it has a primary key column.

SQL> create table test
  2    (id        number primary key,
  3     file_name varchar2(20),
  4     jpeg_img  blob
  5    );

Table created.

Query which looks like yours, i.e. selects file name and the image (contents of the BLOB column) doesn't work, as you already know:

SQL> select distinct
  2    file_name, jpeg_img
  3  from test;
  file_name, jpeg_img
             *
ERROR at line 2:
ORA-00932: inconsistent datatypes: expected - got BLOB

But, if you include the primary key, it works:

SQL> select distinct
  2    id, file_name, jpeg_img
  3  from test;

no rows selected

Of course, it doesn't make much sense because primary key must be unique anyway, so - if you applied such a code - you'd get all rows from the table.

Another option is to calculate BLOB column's length (if that's good enough for youe):

SQL> select distinct
  2    file_name, dbms_lob.getlength(jpeg_img) jpeg
  3  from test;

no rows selected

A better option is to calculate hash:

SQL> select distinct
  2    file_name, dbms_crypto.hash(jpeg_img, 2) jpeg
  3  from test;

no rows selected

SQL>

(Of course, nothing gets selected in my examples as test table is empty; you should get some results).