8 0 CREATE TABLE a ( d Date, os String, n UInt64 ) ENGINE = MergeTree PARTITION BY d ORDER BY (d, n) insert into a select '2000-01-01', ['aa','bb','cc','dd'][number % 4 + 1], number from numbers_mt(10000000) insert into a select '2000-01-02', ['aa','bb','cc','dd'][number % 4 + 1], number from numbers_mt(10000000) insert into a select '2000-01-03', ['aa','bb','cc','dd'][number % 4 + 1], number from numbers_mt(10000000) insert into a select '2000-01-04', ['aa','bb','cc','dd'][number % 4 + 1], number from numbers_mt(10000000) OPTIMIZE TABLE a FINAL select d, count() from a group by d select os, count() from a group by os select d, os, count() from a group by d, os drop table if exists a