Where clause with null values

Question

I need to have a where clause but either/both of the two attributes compared could be null. How can I make this work, atm it just returns no records even though rows do exist.
Thanks

Answer 1

Andrew,
I think you didn't read correctly what I wrote. I said:
"Even if a column is unique you still can have several nulls in it"
So I didnt speak about the case where you have severeal columns in a unique constraint but only ONE.
SQL> CREATE TABLE tab1 (col1 number);
Table created.
SQL> ALTER table tab1 add constraint tab1_col1_uk unique (col1);
Table altered.
SQL> INSERT INTO tab1 VALUES (1);
1 row created.
SQL> INSERT INTO tab1 VALUES (2);
1 row created.
SQL> INSERT INTO tab1 VALUES (2);
INSERT INTO tab1
ERROR at line 1:
ORA-00001: unique constraint (MUELLERMAU.TAB1_COL1_UK) violated
SQL> INSERT INTO tab1 VALUES (NULL);
1 row created.
SQL> INSERT INTO tab1 VALUES (NULL);
1 row created.
And even if you have a unique constraint over several columns you can still have more than on records containing only nulls in all fields related to that unique contraint.
SQL> CREATE TABLE nn (col1 number, col2 varchar2(3));
Table created.
SQL> ALTER TABLE nn ADD CONSTRAINT nn_uk UNIQUE (col1, col2);
Table altered.
SQL> INSERT INTO nn VALUES (NULL,NULL);
1 row created.
SQL> INSERT INTO nn VALUES (NULL,NULL);
1 row created.
Regards
Maurice