drop table if exists test.table;
create table test.table (key UInt64, val UInt64) engine = MergeTree order by key settings index_granularity=8192;
insert into test.table select number, number / 8192 from system.numbers limit 100000; 
alter table test.table add column def UInt64 default val + 1;
select * from test.table prewhere val > 2 format Null;

drop table if exists test.table;
create table test.table (key UInt64, val UInt64) engine = MergeTree order by key settings index_granularity=8192;
insert into test.table select number, number / 8192 from system.numbers limit 100000; 
alter table test.table add column def UInt64;
select * from test.table prewhere val > 2 format Null;