Update record to specific value or to null

Question

Hello.
We have two tables. Both have the same attribute. Update sentence look if attribute has the same value in both tables. If the value is the same, another attribute is updated to specific value in one table.
Now i want to update attribute in all records. But if the both tables haven't got the same value, attribute in record should be updated to null.
For now update looks like:
update tableA set att1 = att2
where att3 = value2 and att4 IN (select att4 from tableB where att2 = value2);
Any idea?
I hope i explained the problem properly.
Thanks.

Answer 1

Like..
SQL> select * from test1;
C1         C2
c1          1
SQL> select * from test2;
C1        C22        C33
c2         11        100
c1          1        100
SQL> update test2 t2
  2  set c33 = decode(c22,(select max(c2) from test1 t1 where t1.c1=t2.c11),0,null);
2 rows updated.
SQL> select * from test2;
C1        C22        C33
c2         11
c1          1          0