text: --create classes,create a vclass,create a vclass based on a created class and inherited from another created class, create a vclass use gropu by function  
  
  
  CREATE CLASS ddl_0001 (
  	int_col int,
  	var_col varchar(20),
  	set_col set(int)
  );
  
  CREATE CLASS ddl_0002 UNDER ddl_0001 (
  	ref_col ddl_0001
  );
  
  CREATE CLASS ddl_0003 UNDER ddl_0002 (
  	ref1_col ddl_0002
  );
  
  CREATE CLASS ddl_0004 UNDER ddl_0003 (
  	ref2_col ddl_0003
  );
  
  CREATE CLASS ddl_0005 UNDER ddl_0004 (
  	ref3_col ddl_0004
  );
  
  CREATE CLASS ddl_0006 UNDER ddl_0005 (
  	ref4_col ddl_0005
  );
  
  CREATE VCLASS ddl_0007 (
  	int_col int,
  	var_col varchar(20),
  	set_col set(int)
  );
  
  CREATE VCLASS ddl_0008 UNDER ddl_0007 
  as
  select a.int_col, a.var_col,a.set_col from ddl_0002 a;
  
  -- group by 
  CREATE VCLASS ddl_0009 UNDER ddl_0007 (
  	int_col int,
  	var_col varchar(20),
  	set_col set(int),
  	ref_col ddl_0005
  ) as
  select Max(a.int_col), a.var_col,a.set_col, a.ref4_col 
  from ddl_0006 a 
  group by a.var_col,a.set_col,a.ref4_col;
  
  
  
  
  drop vclass ddl_0009;
  drop vclass ddl_0008;
  drop vclass ddl_0007;
  drop class ddl_0006;
  drop class ddl_0005;
  drop class ddl_0004;
  drop class ddl_0003;
  drop class ddl_0002;
  drop class ddl_0001;