DROP TABLE IF EXISTS mutation_table; CREATE TABLE mutation_table ( date Date, key UInt64, value String ) ENGINE = MergeTree() PARTITION BY date ORDER BY tuple(); INSERT INTO mutation_table SELECT toDate('2019-10-01'), number, '42' FROM numbers(100); INSERT INTO mutation_table SELECT toDate('2019-10-02'), number, 'Hello' FROM numbers(100); SELECT distinct(value) FROM mutation_table ORDER BY value; ALTER TABLE mutation_table MODIFY COLUMN value UInt64 SETTINGS mutations_sync = 2; --{serverError UNFINISHED} SELECT distinct(value) FROM mutation_table ORDER BY value; --{serverError CANNOT_PARSE_TEXT} KILL MUTATION where table = 'mutation_table' and database = currentDatabase(); ALTER TABLE mutation_table MODIFY COLUMN value String SETTINGS mutations_sync = 2; SELECT distinct(value) FROM mutation_table ORDER BY value; DROP TABLE IF EXISTS mutation_table;