[Oracle] Verify if column has not null check

To test whether a column in an Oracle DB has been declared with a NOT NULL check, it is possible to query the dba_tab_columns table:
 
SELECT nullable
FROM   dba_tab_columns
WHERE  owner       = :owner
  AND  table_name  = :table
  AND  column_name = :column
;





Where owner, table_name and column_name are all upper case. That would output (always in upper case):

N = not nullable
Y  = nullable

This will NOT work if the check is done with a constraint instead