SQL & PL/SQL

Hi

I have the following query:

select uc.table_name

      ,uc.column_name

      ,ucc.constraint_name

      ,uco.search_condition

      ,uc.column_id

from   user_tab_columns  uc

left outer join user_cons_columns ucc on (   uc.table_name  = ucc.table_name

                                         and uc.column_name = ucc.column_name)

left outer join user_constraints  uco on (ucc.constraint_name = uco.constraint_name)

where  uc.table_name = '&&TABLE_NAME'

and  ( uco.constraint_type = 'C' or uco.constraint_type is NOT null)

and 'N' = '&&IS_NULL'

union all

select uc.table_name

      ,uc.column_name

      ,ucc.constraint_name

      ,uco.search_condition

      ,uc.column_id

from   user_tab_columns  uc

left outer join user_cons_columns ucc on (   uc.table_name  = ucc.table_name

                                         and uc.column_name = ucc.column_name)

left outer join user_constraints  uco on (ucc.constraint_name = uco.constraint_name)

where  uc.table_name = '&&TABLE_NAME'

and  ( uco.constraint_type = 'C' or uco.constraint_type is null)

and 'Y' = '&&IS_NULL'

order by column_id;

When I specify "N" for the IS_NULL parameter, then the correct rows appear, but when specifying "Y", then both NULL and NOT null columns appear.

Is there a way I can get only one list or the other ?

for example, for the following table:

CREATE GLOBAL TEMPORARY TABLE TBL_GT (ID INTEGER, X VARCHAR2(10) NOT NULL);

I would like to see only the columns ID if "Y" is specified and only the column X if "N" is specified.