Null value in Composite Primary key

Question

Hi,
I have a requirement where I need to identify each record based on 4 columns. I though that I could achieve the same by imposing a composite primary key based on all the 4 columns. But any one of the column can be null at anytime. Can I still impose a composite primary key? i.e., if I create a composite primary key based on 4 columns, can any one of the column be null?
Your help would be more appreciated.

Answer 1

No, you can't
By definition a Primary Key is NOT NULL
SQL> drop table t
  2  /
Table dropped.
Elapsed: 00:00:00.03
SQL>
SQL> create table t
  2  (col1 number null
  3  ,col2 number null
  4  ,col3 number null
  5  ,col4 number null
  6  ,constraint tpk primary key (col1, col2, col3, col4)
  7  )
  8  /
Table created.
Elapsed: 00:00:00.03
SQL>
SQL> desc t
Name                                                              Null?    Type
COL1                                                              NOT NULL NUMBER
COL2                                                              NOT NULL NUMBER
COL3                                                              NOT NULL NUMBER
COL4                                                              NOT NULL NUMBER
SQL>