MySQL 8.0

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create table foos as select 1 as a union all select 2
create table bars as select 'a' as b
select (select count(*) from foos) as x, (select count(*) as bars) as y, x / y
Unknown column 'x' in 'field list'

select (select count(*) from foos) as x, (select count(*) as bars) as y, (select x / y)


x
y
(select x / y)


2
1
2.0000