drop table if exists z; create table z (pk Int64, d Date, id UInt64, c UInt64) Engine MergeTree partition by d order by pk ; insert into z select number, '2021-10-24', intDiv (number, 10000), 1 from numbers(1000000); optimize table z final; alter table z add projection pp (select id, sum(c) group by id); alter table z materialize projection pp settings mutations_sync=1; SELECT name, partition, formatReadableSize(sum(data_compressed_bytes) AS size) AS compressed, formatReadableSize(sum(data_uncompressed_bytes) AS usize) AS uncompressed, round(usize / size, 2) AS compr_rate, sum(rows) AS rows, count() AS part_count FROM system.projection_parts WHERE database = currentDatabase() and table = 'z' AND active GROUP BY name, partition ORDER BY size DESC; drop table z;