you cannot update with sqlldr.

And an update will update the same set of columns every time (it would be not efficient to go slow by slow and read out a row, determine what columns changed, generate an update just for them, bind to it and execute it).

You could use a MERGE statement and an EXTERNAL TABLE:

ops$tkyte%ORA9IR2> create or replace directory data_dir as '/tmp/'
2 /

Directory created.

ops$tkyte%ORA9IR2> create table external_table
2 (EMPNO NUMBER(4) ,
3 ENAME VARCHAR2(10),
4 JOB VARCHAR2(9),
5 MGR NUMBER(4),
6 HIREDATE DATE,
7 SAL NUMBER(7, 2),
8 COMM NUMBER(7, 2) ,
9 DEPTNO NUMBER(2)
10 )
11 ORGANIZATION EXTERNAL
12 ( type oracle_loader
13 default directory data_dir
14 access parameters
15 ( fields terminated by ',' )
16 location ('emp.dat')
17 )
18 /

Table created.

ops$tkyte%ORA9IR2> !head /tmp/emp.dat
7369,SMITH,CLERK,7902,17-DEC-80,800,,20
7499,ALLEN,SALESMAN,7698,20-FEB-81,1600,300,30
7521,WARD,SALESMAN,7698,22-FEB-81,1250,500,30
7566,JONES,MANAGER,7839,02-APR-81,2975,,20
7654,MARTIN,SALESMAN,7698,28-SEP-81,1250,1400,30
7698,BLAKE,MANAGER,7839,01-MAY-81,2850,,30
7782,CLARK,MANAGER,7839,09-JUN-81,2450,,10
7788,SCOTT,ANALYST,7566,19-APR-87,3000,,20
7839,KING,PRESIDENT,,17-NOV-81,5000,,10
7844,TURNER,SALESMAN,7698,08-SEP-81,1500,0,30

ops$tkyte%ORA9IR2> create table emp
2 as
3 select *
4 from scott.emp
5 where mod(empno,2) = 0
6 /

Table created.

ops$tkyte%ORA9IR2> update emp set sal = sal/2
2 /

10 rows updated.

ops$tkyte%ORA9IR2> commit;

Commit complete.

ops$tkyte%ORA9IR2>
ops$tkyte%ORA9IR2> merge into EMP e1
2 using EXTERNAL_TABLE e2
3 on ( e2.empno = e1.empno )
4 when matched then
5 update set e1.sal = e2.sal
6 when not matched then
7 insert ( empno, ename, job, mgr, hiredate, sal, comm, deptno )
8 values ( e2.empno, e2.ename, e2.job, e2.mgr, e2.hiredate, e2.sal, e2.comm, e2.deptno )
9 /

14 rows merged.

ops$tkyte%ORA9IR2> commit;

Commit complete.


that'll update existing, insert new records.