Using NVL function in subselect of an update

Question

Hi,
nvl is not working in my situation
Here is my select
SELECT nvl(a.id, 'WAS NULL') FROM table_1 a, table_2 b
WHERE a.id=b.id;
Now here I get NULL instead of 'WAS NULL' as I accepted.
Table a and table b do not have any identical ids, still I need to be a value returned.
Is there a way?
Thanks

Answer 1

Well this works for me:
SQL> CREATE TABLE table_1 (id INT NOT NULL, val VARCHAR2(10) NOT NULL);
Table created.
SQL> CREATE TABLE table_2 (id INT NOT NULL, val VARCHAR2(10) NOT NULL);
Table created.
SQL> INSERT INTO table_1 VALUES (1, 'A');
1 row created.
SQL> INSERT INTO table_2 VALUES (2, 'B');
1 row created.
SQL> UPDATE table_1 t1
  2  SET    val =
  3         ( SELECT NVL(t2.val,'Was NULL') FROM table_2 t2
  4           WHERE  t2.id = t1.id );
SET    val =
ERROR at line 2:
ORA-01407: cannot update ("WILLIAM"."TABLE_1"."VAL") to NULL
SQL> UPDATE table_1 t1
  2  SET    val =
  3         NVL
  4         ( ( SELECT t2.val
  5             FROM   table_2 t2
  6             WHERE  t2.id = t1.id )
  7         , 'Was NULL');
1 row updated.
SQL> SELECT * FROM table_1;
        ID VAL
         1 Was NULL
1 row selected.