SELECT DISTINCT CLOB_COLUMN FROM TABLE;

Question

I would like to find the distinct CLOB values that can assume the column called CLOB_COLUMN (of type CLOB) contained in the table called COPIA.

I have selected a PROCEDURAL WAY to solve this problem, but I would prefer to give a simple SELECT as the following: SELECT DISTINCT CLOB_COLUMN FROM TABLE avoiding the error "ORA-00932: inconsistent datatypes: expected - got CLOB"

How can I achieve this?

Thank you in advance for your kind cooperation. This is the procedural way I've thought:

-- Find the distinct CLOB values that can assume the column called CLOB_COLUMN (of type CLOB)
-- contained in the table called COPIA
-- Before the execution of the following PL/SQL script, the CLOB values (including duplicates) 
-- are contained in the source table, called S1
-- At the end of the excecution of the PL/SQL script, the distinct values of the column called CLOB_COLUMN
-- can be find in the target table called S2

BEGIN
   EXECUTE IMMEDIATE 'TRUNCATE TABLE S1 DROP STORAGE';

   EXECUTE IMMEDIATE 'DROP TABLE S1 CASCADE CONSTRAINTS PURGE';
EXCEPTION
   WHEN OTHERS
   THEN
      BEGIN
         NULL;
      END;
END;

BEGIN
   EXECUTE IMMEDIATE 'TRUNCATE TABLE S2 DROP STORAGE';

   EXECUTE IMMEDIATE 'DROP TABLE S2 CASCADE CONSTRAINTS PURGE';
EXCEPTION
   WHEN OTHERS
   THEN
      BEGIN
         NULL;
      END;
END;

CREATE GLOBAL TEMPORARY TABLE S1
ON COMMIT PRESERVE ROWS
AS
   SELECT CLOB_COLUMN FROM COPIA;

CREATE GLOBAL TEMPORARY TABLE S2
ON COMMIT PRESERVE ROWS
AS
   SELECT *
     FROM S1
    WHERE 3 = 9;

BEGIN
   DECLARE
      CONTEGGIO   NUMBER;

      CURSOR C1
      IS
         SELECT CLOB_COLUMN FROM S1;

      C1_REC      C1%ROWTYPE;
   BEGIN
      FOR C1_REC IN C1
      LOOP
         -- How many records, in S2 table, are equal to c1_rec.clob_column?
         SELECT COUNT (*)
           INTO CONTEGGIO
           FROM S2 BETA
          WHERE DBMS_LOB.
                 COMPARE (BETA.CLOB_COLUMN,
                          C1_REC.CLOB_COLUMN) = 0;

         -- If it does not exist, in S2, a record equal to c1_rec.clob_column, 
         -- insert c1_rec.clob_column in the table called S2
         IF CONTEGGIO = 0
         THEN
            BEGIN
               INSERT INTO S2
                    VALUES (C1_REC.CLOB_COLUMN);

               COMMIT;
            END;
         END IF;
      END LOOP;
   END;
END;

Answer 1

If it is acceptable to truncate your field to 32767 characters this works:

select distinct dbms_lob.substr(FIELD_CLOB,32767) from Table1