根据子查询的查询结果声明变量

Question

I am pretty new in this field and I'd like to know if it's possible and how to fix this code that I wrote:

begin;

DECLARE @income BIGINT;
DECLARE @outcome BIGINT;

set @income = (select cars_carID as y, (sum(datediff(returndate,rentdate)) * dayprice from rentals,cars where cars_carID= y) group by carID);

set @outcome=(select carID as x, (sum(maint_price) from maintenance,cars where Maint_carID = x) group by maint_carID);

select @income-@outcome;

end;

The queries are ok but it keep giving me few errors on variables and writing a combination of queries like:

Select 
Cars_carID as x, 
(
    select 
    (
        select (sum(datediff(returndate,rentdate)) * dayprice)-(sum(Maint_Price)  
        from rentals, cars, maintenance 
        where cars_carID=carID 
            and Maint_carID = x 
        group by carID
    )
)

it's neverending.

Answer 1

For start you have this problem :
Your query gets 2 values and want to store them in one variable.
That does not work.

DECLARE @income BIGINT; 
DECLARE @outcome BIGINT;

set @income = (select cars_carID as y, 
                      (sum(datediff(returndate,rentdate)) * dayprice) 
               from rentals,
                    cars 
               where cars_carID= y
               group by carID
              );

Change it to something like this :

set @income = (select (sum(datediff(returndate,rentdate)) * dayprice) 
               from rentals
                 inner join cars on rentals.carID = cars.CarID
               group by carID
              );

This query will still not run because carID is in the group by and not in the select clause, but without knowning exactly what you need I cant complete the query.
It should be able to get you on your way though

Maybe it should be like this

set @income = select sum(t.result)
              from   (select cars.carID,    
                             (sum(datediff(returndate,rentdate)) * dayprice) as result 
                      from rentals
                        inner join cars on rentals.carID = cars.CarID
                      group by carID
                    ) t