constraints in create table..

hi all,
 

do anybody explain me what is
happening when i'm creating a table with the following constraints..
 

CREATE TABLE
TAB1(
ENUM NUMBER PRIMARY KEY
CHECK(ENUM IS NULL),
ENAME
VARCHAR2(10)
);
 

why i'm being able to create
table with such contradicting constraints. both can't be true at the
same time.
i can't have null in aprimary
key.
 

what's the significance of
this DDL.
 

thanks in
advance..
 

Saurabh
Sharma Received on Wed Aug 29 2001 - 13:00:13 CDT