size 10000000 50000000 table numbers numbers_mt create table t_str_key_{size}(a String, b FixedString(25)) engine=MergeTree order by tuple() insert into t_str_key_{size} select toString(number) as s, toFixedString(s, 25) from numbers_mt({size}) select a from t_str_key_{size} group by a format Null select b from t_str_key_{size} group by b format Null select number from {table}({size}) group by number format Null select count() from {table}({size}) group by number format Null select number from numbers_mt(1e8) group by number format Null select count() from numbers_mt(1e8) group by number format Null drop table t_str_key_{size}