create table foo(A Int64, V Int64, S String) Engine=MergeTree partition by V order by A;
insert into foo select number, number%5, '' from numbers(100000);
create table foo_merge as foo ENGINE=Merge(currentDatabase(), '^foo');

select count(), B from foo_merge join 
   (select materialize('') as S, 5 B) x using S 
where V = 4 
group by B

Key condition: unknown
MinMax index condition: unknown
Selected 5 parts by date, 5 parts by key, 15 marks by primary key, 15 marks to read from 5 ranges

Processed 100.00 thousand rows

select count(), B from foo_merge join 
   (select materialize('') as S, 5 B) x using S 
where V = 4 and A = 4 
group by B 

Key condition: unknown
MinMax index condition: unknown
Selected 5 parts by date, 5 parts by key, 15 marks by primary key, 15 marks to read from 5 ranges

Processed 100.00 thousand rows

select count(), B from foo join 
   (select materialize('') as S, 5 B) x using S 
where V = 4 and A = 4 
group by B 

Key condition: unknown, (column 0 in [4, 4]), and
MinMax index condition: (column 0 in [4, 4]), unknown, and
Selected 1 parts by date, 1 parts by key, 1 marks by primary key, 1 marks to read from 1 ranges
Processed 8.19 thousand rows

select count(), B from (select * from foo_merge) f join 
   (select materialize('') as S, 5 B) x using S 
where V = 4 and A = 4 
group by B 

Key condition: (column 0 in [4, 4]), unknown, and
MinMax index condition: unknown, (column 0 in [4, 4]), and
Selected 1 parts by date, 1 parts by key, 1 marks by primary key, 1 marks to read from 1 ranges
Processed 8.19 thousand rows