All_tab_columns says NULLABLE = 'Y' while there is a NOT NULL constraint

Question

Hi all,
I created a table MANT (here is the script) :
CREATE TABLE DMI.MANT
  MANT     NUMBER(7)                            NOT NULL,
  SPER     NUMBER(7)                            NOT NULL,
  RANT     VARCHAR2(10 BYTE)                    NOT NULL,
  ANT      VARCHAR2(200 BYTE),
  CMT      VARCHAR2(800 BYTE),
  PERIODE  VARCHAR2(200 BYTE),
  DU       DATE,
  USR      VARCHAR2(10 BYTE),
  DTE      DATE
)Then I added a column called RSMF :
ALTER TABLE DMI.MANT
ADD (RSMF VARCHAR2(100 BYTE));and added a check constraint :
ALTER TABLE DMI.MANT ADD
CONSTRAINT RSMF_NOT_NULL
CHECK (RSMF IS NOT NULL)
ENABLE
NOVALIDATEI had to add NOVALIDATE clause because all the records had a null value. So to validate the constraint I simply executed the following update
update dmi.mant set rsmf = 'yy';and then validate the contraint with :
ALTER TABLE DMI.MANT
MODIFY CONSTRAINT RSMF_NOT_NULL
VALIDATE;The problem comes when I query ALL_TAB_COLUMNS table...
Select OWNER,TABLE_NAME,COLUMN_NAME,DATA_TYPE,DATA_LENGTH,NULLABLE
from all_tab_columns
where table_name = 'MANT'
   and owner = 'DMI'
   and COLUMN_NAME = 'RSMF';Why does the ALL_TAB_COLUMNS table gives for RSMF column a NULLABLE value equals to 'Y' while there is a validated check NOT NULL constraint on it ?
It's annoying because I want to get all the NOT NULL columns in a given table and here the SRMF column is not returned...
Here is the result :
OWNER  |TABLE_NAME |COLUMN_NAME  |DATA_TYPE  |DATA_LENGTH  |NULLABLE
DMI    |MANT       |RSMF         |VARCHAR2   |100          |YThks for your replies...

Answer 1

NULLABLE would be true if you created the table like this:
create table x (a not null)
but not if you add a check constraint after the fact.