text: -- create class and add pk when instances are exist
  
  create class aoo ( a NUMERIC, b int, c int );
  
  insert into aoo values (1,2,2);
  
  alter class aoo add primary key(a);
  
  select attr_name, is_nullable from db_attribute where class_name = 'aoo' order by 1,2;
  
  select * from db_index where class_name = 'aoo';
  
  select * from aoo;
  
  drop aoo;