text: SET max_threads=16;
  SELECT 'filter push down: push (number+1) to filter';
  EXPLAIN SELECT (number+1) as a from numbers_mt(10000) where a > 2;
  
  SELECT 'limit push down: push (limit 10) to projection';
  EXPLAIN select (number+1) as c1, number as c2 from numbers_mt(10000) where (c1+c2+1)=1 limit 10;
  
  SELECT 'group by push down: push alias to group by';
  EXPLAIN select (number+1) as c1, (number%3+1) as c2 from numbers_mt(10000) group by c2;
  
  SELECT 'projection push down: push (name and value) to readdatasource';
  EXPLAIN select name from system.settings where value > 10;
  