1 1 256 0 256 size 100000 1000000 10000000 partitions 16 32 64 create table t_{size}_{partitions}(a UInt64) engine=MergeTree order by a partition by sipHash64(a) % {partitions} insert into t_{size}_{partitions} select * from numbers_mt({size}) optimize table t_{size}_{partitions} final select a from t_{size}_{partitions} group by a format Null select a from t_{size}_{partitions} group by a format Null settings optimize_aggregation_in_order = 1 drop table t_{size}_{partitions}