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;

user_11292046 · Answer

add TO_CHAR after distinct keyword to convert CLOB to CHAR

SELECT DISTINCT TO_CHAR(CLOB_FIELD) from table1;   //This will return distinct values in CLOB_FIELD

user_1485955 · Answer

If truncating the clob to the size of a varchar2 won't work, and you're worried about hash collisions, you can:

Add a row number to every row;
Use DBMS_lob.compare in a not exists subquery. Exclude duplicates (this means: compare = 0) with a higher rownum.

For example:

create table t (
  c1 clob
);

insert into t values ( 'xxx' );
insert into t values ( 'xxx' );
insert into t values ( 'yyy' );

commit;

with rws as (
   select row_number () over ( order by rowid ) rn,
          t.*
   from   t
)
  select c1 from rws r1
  where  not exists (
    select * from rws r2
    where  dbms_lob.compare ( r1.c1, r2.c1 ) = 0
    and    r1.rn > r2.rn
  );

C1    
xxx   
yyy

user_3768804 · Answer

I know this is an old question but I believe I've figure out a better way to do what you are asking.

It is kind of like a cheat really...The idea behind it is that You can't do a DISTINCT of a Clob column but you can do a DISTINCT on a Listagg function of a Clob_Column...you just need to play with the partition clause of the Listagg function to make sure it will only return one value.

With that in mind...here is my solution.

SELECT DISTINCT listagg(clob_column,'| ') within GROUP (ORDER BY unique_id) over (PARTITION BY unique_id) clob_column 
 FROM copia;

SELECT DISTINCT CLOB_COLUMN FROM TABLE;

8 Answers