drop table if exists merge_tree; set allow_deprecated_syntax_for_merge_tree=1; create table merge_tree ( CounterID UInt32, StartDate Date, Sign Int8, VisitID UInt64, UserID UInt64, StartTime DateTime, ClickLogID UInt64) ENGINE = CollapsingMergeTree(StartDate, intHash32(UserID), tuple(CounterID, StartDate, intHash32(UserID), VisitID, ClickLogID), 8192, Sign); insert into merge_tree values (1, '2013-09-19', 1, 0, 2, '2013-09-19 12:43:06', 3); alter table merge_tree add column dummy String after CounterID; describe table merge_tree; insert into merge_tree values (1, 'Hello, Alter Table!','2013-09-19', 1, 0, 2, '2013-09-19 12:43:06', 3); select CounterID, dummy from merge_tree where dummy <> '' limit 10; alter table merge_tree drop column dummy; describe table merge_tree; drop table merge_tree;