DROP TABLE IF EXISTS t_sparse_detach; CREATE TABLE t_sparse_detach(id UInt64, s String) ENGINE = MergeTree ORDER BY id SETTINGS ratio_of_defaults_for_sparse_serialization = 0.9; INSERT INTO t_sparse_detach SELECT number, number % 21 = 0 ? toString(number) : '' FROM numbers(10000); INSERT INTO t_sparse_detach SELECT number, number % 21 = 0 ? toString(number) : '' FROM numbers(10000); OPTIMIZE TABLE t_sparse_detach FINAL; SELECT count() FROM t_sparse_detach WHERE s != ''; SELECT column, serialization_kind FROM system.parts_columns WHERE table = 't_sparse_detach' AND database = currentDatabase() AND active ORDER BY column; DETACH TABLE t_sparse_detach; ATTACH TABLE t_sparse_detach; SELECT count() FROM t_sparse_detach WHERE s != ''; SELECT column, serialization_kind FROM system.parts_columns WHERE table = 't_sparse_detach' AND database = currentDatabase() AND active ORDER BY column; TRUNCATE TABLE t_sparse_detach; ALTER TABLE t_sparse_detach MODIFY SETTING vertical_merge_algorithm_min_rows_to_activate = 1, vertical_merge_algorithm_min_columns_to_activate = 1; INSERT INTO t_sparse_detach SELECT number, number % 21 = 0 ? toString(number) : '' FROM numbers(10000); INSERT INTO t_sparse_detach SELECT number, number % 21 = 0 ? toString(number) : '' FROM numbers(10000); OPTIMIZE TABLE t_sparse_detach FINAL; SELECT count() FROM t_sparse_detach WHERE s != ''; SELECT column, serialization_kind FROM system.parts_columns WHERE table = 't_sparse_detach' AND database = currentDatabase() AND active ORDER BY column; DETACH TABLE t_sparse_detach; ATTACH TABLE t_sparse_detach; SELECT count() FROM t_sparse_detach WHERE s != ''; SELECT column, serialization_kind FROM system.parts_columns WHERE table = 't_sparse_detach' AND database = currentDatabase() AND active ORDER BY column; DROP TABLE t_sparse_detach;