text: create table num_t(one int, zero int, null_c int, unk_c int);
  
  insert into num_t values (1, 0, NULL, UNKNOWN);
  
  select 1 from num_t where one IS TRUE;
  select 1 from num_t where one IS FALSE;
  select 1 from num_t where one IS UNKNOWN;
  select 1 from num_t where zero IS TRUE;
  select 1 from num_t where zero IS FALSE;
  select 1 from num_t where zero IS UNKNOWN;
  select 1 from num_t where null_c IS TRUE;
  select 1 from num_t where null_c IS FALSE;
  select 1 from num_t where null_c IS UNKNOWN;
  select 1 from num_t where unk_c IS TRUE;
  select 1 from num_t where unk_c IS FALSE;
  select 1 from num_t where unk_c IS UNKNOWN;
  
  select 1 from num_t where not(one IS TRUE);
  
  drop table num_t;
  