I have written a query as follows :
select
a.x1,
a.x2,
b.x3
from
(select x1,x2,x4 from table1 where 'some conditions') as a
inner join
(select x3,x4 from table2) as b
on
a.x3=b.x3
 
I have another version as :
select
a.x1,
a.x2,
b.x3
from

Hello,

I have several questions about the delay in execution of this query.

How do we calculate the cost of a Query? could it be calculated in numbers? then what is the unit of measurement?