Help requested: WHAT IS WRONG WITH THIS sql?

Question

I have two tables
TABLE1
ORG VARCHAR2(1)
EMPNO VARCHAR2(10)
UNION_DUES NUMBER(7,2)
UNION_CODE VARCHAR2(5)
TABLE2
ORG VARCHAR2(1)
EMPNO VARCHAR2(10)
YEAR NUMBER(4)
CODE2 VARCHAR2(5)
EMPLOYEE_FIXED_AMOUNT NUMBER (7,2)
****** WHAT DO I WANT TO DO *****
there is one entry for each employee in TABLE1. There are multiple entries for each employee in TABLE2. I want to update TABLE2 for all the employees in TABLE1.
But only update those entries in TABLE2 where CODE2 = UNION_CODE and YEAR = 2002.
***** MY SQL ******
update TABLE2
set employee_fixed_amount =
(select union_dues from TABLE1
WHERE TABLE2.EMPNO = TABLE1.empno
and TABLE2.org = TABLE1.org
and TABLE2.code2 = TABLE1.union_code)
where year = 2002;
**** ORACLE ERROR PRODUCED ****
ora-01407cannot update (table2.employee_fixed_amount) to null

Answer 1

Either you have a NULL value for table1.union_dues or there is no match in table1 based on your criteria. So, you can check for these by:
update TABLE2
   set employee_fixed_amount =
         (select union_dues
            from TABLE1
           where TABLE2.EMPNO = TABLE1.empno
             and TABLE2.org = TABLE1.org
             and TABLE2.code2 = TABLE1.union_code)
where year = 2002
   and exists (select null
                 from table1
                where table1.empno = table2.empno
                  and table1.org = table2.org
                  and table1.union_code = table2.code2
                  and table1.union_dues is not null);or, if it is alright that the employee_fixed_amount be set to 0 when there is no match or the union_dues is NULL, then:
update TABLE2
   set employee_fixed_amount =
         nvl((select union_dues
                from TABLE1
               where TABLE2.EMPNO = TABLE1.empno
                 and TABLE2.org = TABLE1.org
                 and TABLE2.code2 = TABLE1.union_code), 0)
where year = 2002;