How to convert clob to varchar2 in an update trigger

Question

Hi,
I need to convert a field (clob) to varchar2 in a update trigger, how can I do that?
regards.

Answer 1

The maximum amount of data you can store in CLOB column is 4GB.
You have table TABLE1 having col1 CLOB datatype.You have one more table
Table_audit_1 without having CLOB datatype column and want to move CLOB
data into VARCHAR2 column which has maximum length of 4000 and want to
audit col1 CLOB into VARCHAR2.It seems to me you dont care about the data
beyond 4000 bytes.
In 9i SUBSTR, INSTR can be performed without reference to the DBMS_LOB
package.
SQL> DROP TABLE mytable
  2  /
Table dropped.
SQL> DROP TABLE mytable1
  2  /
Table dropped.
SQL> CREATE TABLE mytable
  2  (a   NUMBER,b   CLOB)
  3  /
Table created.
SQL> CREATE TABLE mytable1
  2  (c  NUMBER,d   VARCHAR2(4000))
  3  /
Table created.
SQL> DECLARE
  2      loc           CLOB;
  3  BEGIN
  4      FOR i IN 1..5000
  5      LOOP
  6        loc:=loc||i;
  7      END LOOP;
  8      INSERT INTO mytable  (a,b) VALUES (1,loc);
  9      INSERT INTO mytable1 (c,d) VALUES (1,SUBSTR(loc,1,4000));
10      COMMIT;
11  END;
12  /
PL/SQL procedure successfully completed.
SQL> SET LONG 5000
SQL> CREATE OR REPLACE TRIGGER mytrigger BEFORE UPDATE ON mytable FOR EACH ROW
  2  BEGIN
  3      UPDATE mytable1
  4         SET d=SUBSTR(:NEW.b,1,4000)
  5       WHERE c=:NEW.a;
  6  END;
  7  /
Trigger created.
SQL> DECLARE
  2      loc           CLOB;
  3  BEGIN
  4      FOR i IN 1..1000
  5      LOOP
  6        loc:=loc||'A '||i;
  7      END LOOP;
  8      UPDATE mytable
  9         SET b=loc
10       WHERE a=1;
11      COMMIT;
12  END;
13  /
PL/SQL procedure successfully completed.
SQL> SELECT LENGTH(b) FROM mytable
  2  /
LENGTH(B)
      4893
SQL> SELECT LENGTH(d) FROM mytable1
  2  /
LENGTH(D)
      4000
SQL> Khurram