insert into MyClobTable(ID,Data) values ('101','A string containing more than 40000 characters...')

SQL> CREATE TABLE myClob
  2  (id NUMBER PRIMARY KEY,
  3   clob_data CLOB);

Table created.

SQL>
SQL> INSERT INTO myClob VALUES (101,null);

1 row created.

SQL>
SQL> declare
  2    clob_pointer CLOB;
  3    v_buf VARCHAR2(1000);
  4    Amount BINARY_INTEGER :=1000;
  5    Position INTEGER :=1;
  6  BEGIN
  7    v_buf :=rpad('A',1000,'A');
  8
  9    insert into myClob values (1 ,EMPTY_CLOB());
 10
 11    commit;
 12
 13    SELECT clob_data INTO clob_pointer FROM myClob WHERE id = 1 FOR UPDATE;
 14    DBMS_LOB.OPEN (clob_pointer,DBMS_LOB.LOB_READWRITE);
 15
 16    FOR i IN 1..500 LOOP
 17
 18      DBMS_LOB.WRITE (clob_pointer,Amount,Position,v_buf);
 19
 20      Position :=Position +Amount;
 21
 22    END LOOP;
 23
 24    DBMS_LOB.CLOSE (clob_pointer);
 25
 26  END;
 27  /

PL/SQL procedure successfully completed.

SQL>
SQL> drop table myClob;

Table dropped.

SQL>

insert into Table(Id,Data) values(101,'First 4000 chars')

update Table set Data = Data || 'Next 4000 chars' where DATA like 'First 4000 chars'