Can we use select in FROM clause of SQL select?

Answer 1

create table x(i int identity, 
               a char(1))
insert into x values ('a')
insert into x values ('b')
insert into x values ('c')
insert into x values ('d')
select * from x

update x
set a = b.a
from (select max(a) as a from x) b 
where i > 2

select * from x
drop table x