explain
select distinct key, "" as dummy1, "" as dummy2 from src tablesample (10 rows);

select distinct key, "" as dummy1, "" as dummy2 from src tablesample (10 rows);

explain
create table dummy as
select distinct key, "X" as dummy1, "X" as dummy2 from src tablesample (10 rows);

create table dummy as
select distinct key, "X" as dummy1, "X" as dummy2 from src tablesample (10 rows);

select key,dummy1,dummy2 from dummy;