set allow_experimental_low_cardinality_type = 1; create table test.tab (a String, b LowCardinality(UInt32)) engine = MergeTree order by a; insert into test.tab values ('a', 1); select *, toTypeName(b) from test.tab; alter table test.tab modify column b UInt32; select *, toTypeName(b) from test.tab; alter table test.tab modify column b LowCardinality(UInt32); select *, toTypeName(b) from test.tab; alter table test.tab modify column b StringWithDictionary; select *, toTypeName(b) from test.tab; alter table test.tab modify column b LowCardinality(UInt32); select *, toTypeName(b) from test.tab; alter table test.tab modify column b String; select *, toTypeName(b) from test.tab; alter table test.tab modify column b LowCardinality(UInt32); select *, toTypeName(b) from test.tab; drop table if exists test.tab;