Modify multiple tables and columns to be nullable

declare
  col_name varchar2(30);
begin
  for r in (
  
  select 
    table_name,
    search_condition
  from 
    user_tables t join
    user_constraints c using (table_name)
  where 
    table_name like 'T\_%' escape '\' and
    c.constraint_type = 'C'
  
  ) loop
  
   if r.search_condition like '% IS NOT NULL' then
     col_name := regexp_replace(r.search_condition, '"([^"]*)" IS NOT NULL', '\1');
   
     dbms_output.put_line(col_name);
   
     execute immediate 'alter table ' || r.table_name || ' modify ' || col_name || ' null';
   else
     dbms_output.put_line(r.search_condition);
   end if;
  
  end loop;

end;
/