text: -- [er]create class and add primary key on MULTISET data type
  
  create class aoo ( a MULTISET primary key, b int, c int );
  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;