Script or query to generate a report of null or not null columns

Question

I need a script/query it should pick up all the tables from user_tab_columns and produce a report for all the tables which are the columns are null and not null.

Answer 1

As long as the columns were defined as NOT NULL on table create, or ALTERed NOT NULL, you can do this:
SQL> CREATE TABLE t (id NUMBER NOT NULL, descr VARCHAR2(10));
Table created.
SQL> SELECT column_name, table_name, nullable
  2  FROM user_tab_columns
  3  WHERE table_name = 'T';
COLUMN_NAME                    TABLE_NAME                     N
ID                             T                              N
DESCR                          T                              Y
SQL> ALTER TABLE t modify (descr NOT NULL);
Table altered.
SQL> SELECT column_name, table_name, nullable
  2  FROM user_tab_columns
  3  WHERE table_name = 'T';
COLUMN_NAME                    TABLE_NAME                     N
ID                             T                              N
DESCR                          T                              NNote that if you do:
ALTER TABLE t ADD CONSTRAINT id_nn CHECK (id IS NOT NULL);then the nullable column in xxx_tab_columns will remain as Y.
HTH
John