NULLABLE column is not updated after the NOT NULL constraint definition...

Question

Hi,
SQL> select column_name,nullable from all_tab_columns where table_name='EMP';
COLUMN_NAME                    NULLABLE
EMPNO                          N
ENAME                          Y
JOB                            Y
MGR                            Y
HIREDATE                       Y
SAL                            Y
COMM                           Y
DEPTNO                         Y
CODE_POLEIS_DIAM               Y
9 rows selected
SQL> ALTER TABLE EMP add constraint emp_job_nn check(job is not null);
Table altered
SQL> select constraint_name from all_cons_columns
  2  where table_name='EMP';
CONSTRAINT_NAME
FK_DEPTNO
PK_EMP
EMP_JOB_NN
SQL> select column_name,nullable from all_tab_columns where table_name='EMP';
COLUMN_NAME                    NULLABLE
EMPNO                          N
ENAME                          Y
JOB                            Y                         <---------'NULL'
MGR                            Y
HIREDATE                       Y
SAL                            Y
COMM                           Y
DEPTNO                         Y
CODE_POLEIS_DIAM               Y
9 rows selected
Why is not updated....????
In Oracle ebook:
Oracle® Database Reference
10g Release 2 (10.2)
Part Number B14237-02
the comments about the NULLBLE column are as follows:
"Specifies whether a column allows NULLs. Value is N if there is a NOT NULL constraint on the column or if the column is part of a PRIMARY KEY. The constraint should be in an ENABLE VALIDATE state."
BUT BY DEFAULT ALL CONSTRAINTS ARE IN VALIDATE STATE
(Ref: Oracle® Database SQL Reference
10g Release 2 (10.2)
Part Number B14200-02 )Note : I use OraDB 10g v.2
Thanks a lot
Sim

Answer 1

Hi,
Tom Kytes answer it before:
SQL> create table t ( id int );
Table created.
SQL> desc t
Name                            Null?    Type
ID                                       NUMBER(38)
SQL> alter table t add constraint t_nn check (id is not null);
Table altered.
SQL> insert into t (id) values (null);
insert into t (id) values (null)
ERROR at line 1:
ORA-02290: check constraint (TANDREWS.T_NN) violated
SQL> desc t
Name                            Null?    Type
ID                                       NUMBER(38)
Followup July 16, 2003 - 10am US/Eastern:
that is not a NOT NULL constraint, that is a check constraint
ops$tkyte@ORA920LAP> create table t ( x int );
Table created.
ops$tkyte@ORA920LAP> alter table t modify x not null;
Table altered.
ops$tkyte@ORA920LAP> set linesize 50
ops$tkyte@ORA920LAP> desc t
Name                    Null?    Type
X                       NOT NULL NUMBER(38)To see the full thread in asktom, please refer to:
- http://asktom.oracle.com/pls/asktom/f?p=100:11:0::::P11_QUESTION_ID:1338402651192
Cheers,
Francisco Munoz Alvarez
http://www.oraclenz.com