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;
Use this approach. In table profile column content is NCLOB. I added the where clause to reduce the time it takes to run which is high,
with
r as (select rownum i, content from profile where package = 'intl'),
s as (select distinct (select min(i) from r where dbms_lob.compare(r.content, t.content) = 0) min_i from profile t where t.package = 'intl')
select (select content from r where r.i = s.min_i) content from s
;
It is not about to win any prizes for efficiency but should work.
You could compare the hashes of the CLOB to determine if they are different:
SELECT your_clob
FROM your_table
WHERE ROWID IN (SELECT MIN(ROWID)
FROM your_table
GROUP BY dbms_crypto.HASH(your_clob, dbms_crypto.HASH_SH1))
Edit:
The HASH
function doesn't guarantee that there will be no collision. By design however, it is really unlikely that you will get any collision. Still, if the collision risk (<2^80?) is not acceptable, you could improve the query by comparing (with dbms_lob.compare
) the subset of rows that have the same hashes.
If it is acceptable to truncate your field to 32767 characters this works:
select distinct dbms_lob.substr(FIELD_CLOB,32767) from Table1
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
select distinct DBMS_LOB.substr(column_name, 3000) from table_name;
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
To bypass the oracle error, you have to do something like this :
SELECT CLOB_COLUMN FROM TABLE COPIA C1 WHERE C1.ID IN (SELECT DISTINCT C2.ID FROM COPIA C2 WHERE ....)
来源:https://stackoverflow.com/questions/3921982/select-distinct-clob-column-from-table