Sql Server - Variables inside select - sql

Question

there's any way to declare and use variables INSIDE a select statement?
my idea is to use several times the same nested select for diferent math operations.
i'm using SQL Server 2008 R2 and here is some example:
--Example Table
declare #product_table table(id int, name varchar(20), price int, active bit)
insert into #product_table
values
(1,'productA',100,1),
(2,'productB',50,1),
(3,'productC',20,0),
(4,'productD',300,1),
(5,'productE',80,0)
select
name,
(select sum(price) from #product_table where active = 1), -- <-- Declare this as a Variable
(select sum(price) from #product_table where active = 1),
(select sum(price) from #product_table where active = 1/ price),
(select sum(price) from #product_table where active = 0)
from #product_table

Answer 1

You can use a CTE for this:
;WITH cte AS
(
SELECT (select sum(price) from #product_table where active = 1) AS Sum1
,(select sum(price) from #product_table where active = 0) AS Sum0
)
select
name,
Sum1,
Sum1 / price,
sum0
from #product_table
cross join cte;
The CTE will return one single row thus CROSS JOIN will just add it to the result set.
If you need computed values depending on row-values, you can reach something similar with CROSS APPLY to calculate values row-by-row and use them with a speaking name.
Just to show the principles. If your computation would include some row values, you can use cross apply to get variables:
select
name,
Sum1,
Sum1 / price,
sum0
from #product_table
cross apply
(
SELECT (select sum(price) from #product_table where active = 1) AS Sum1
,(select sum(price) from #product_table where active = 0) AS Sum0
) A

Answer 2

Simply your query using window functions:
select name,
sum(case when active = 1 then price end) over () as price_1,
sum(case when active = 1 then price end) over () / price as ratio,
sum(case when active = 0 then price end) over () as price_0
from #product_table;
You can do what you want using subqueries or CTEs. However, you should learn to use the best functions for what you want to do.

Answer 3

You cannot Declare a Variable Inside a SELECT Statement, but Instead, you can Declare it outside and use it in the SELECT. Like this :
declare #product_table table(id int, name varchar(20), price int, active bit)
DECLARE #SumPrice1 INT,#SumPrice0 INT
insert into #product_table
values
(1,'productA',100,1),
(2,'productB',50,1),
(3,'productC',20,0),
(4,'productD',300,1),
(5,'productE',80,0)
SELECT
#SumPrice1 = sum(price)
from #product_table where active = 1
SELECT
#SumPrice0 = sum(price)
from #product_table where active = 0
select
name,
#SumPrice1,
#SumPrice1,
(#SumPrice1/ price),
#SumPrice0
from #product_table
Or Like This
;WITH CTE
AS
(
SELECT
active,
SumAmt = SUM(price)
FROM #product_table
GROUP BY active
)
SELECT
PT.[Name],
[1] SumAmt,
[1] SumAmt,
[1] /price SumAmtPrice,
[0] ZeroSum
FROM #product_table PT
JOIN CTE
PIVOT
(
SUM(SumAmt)
FOR
Active IN
(
[0],[1]
)
)P
ON 1=1
Or More Simply Like This
SELECT
[name],
SUM(CASE Active WHEN 1 THEN Price ELSE 0 END) OVER(PARTITION BY Active) ActiveSum,
SUM(CASE Active WHEN 0 THEN Price ELSE 0 END) OVER(PARTITION BY Active) ZeroSum
FROM #product_table