DROP TABLE IF EXISTS mt_table; CREATE TABLE mt_table (d Date, key UInt64, data String) ENGINE = MergeTree() PARTITION BY toYYYYMM(d) ORDER BY key; CHECK TABLE mt_table; INSERT INTO mt_table VALUES (toDate('2019-01-02'), 1, 'Hello'), (toDate('2019-01-02'), 2, 'World'); CHECK TABLE mt_table; INSERT INTO mt_table VALUES (toDate('2019-01-02'), 3, 'quick'), (toDate('2019-01-02'), 4, 'brown'); SELECT '========'; CHECK TABLE mt_table; OPTIMIZE TABLE mt_table FINAL; SELECT '========'; CHECK TABLE mt_table; SELECT '========'; INSERT INTO mt_table VALUES (toDate('2019-02-03'), 5, '!'), (toDate('2019-02-03'), 6, '?'); CHECK TABLE mt_table; SELECT '========'; INSERT INTO mt_table VALUES (toDate('2019-02-03'), 7, 'jump'), (toDate('2019-02-03'), 8, 'around'); OPTIMIZE TABLE mt_table FINAL; CHECK TABLE mt_table PARTITION 201902; DROP TABLE IF EXISTS mt_table;