Setting multiple variables' value in one IIF() of a SELECT statement - sql

Question

I have a CROSS JOIN query that I am using to see which combination of item quantities yield the best output.
DECLARE #last_found DECIMAL(10, 2) = 0
DECLARE #calculated DECIMAL(10, 2)
DECLARE #n_count INT
DECLARE #tbl1n INT
DECLARE #tbl2n INT
DECLARE #tbl3n INT
DROP TABLE IF EXISTS #tbl1
DROP TABLE IF EXISTS #tbl2
DROP TABLE IF EXISTS #tbl3
;WITH numbers AS (
SELECT ROW_NUMBER() OVER (ORDER BY [value]) AS n
FROM string_split('1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20', ',')
)
SELECT n, (n * 10000 * (1 + IIF(n > 1, (0.50/19.00) * (n - 1), 0))) AS price
INTO #tbl1 FROM numbers
;WITH numbers AS (
SELECT ROW_NUMBER() OVER (ORDER BY [value]) AS n
FROM string_split('1,2,3,4,5,6,7,8,9,10,11,12', ',')
)
SELECT n, (n * 15000 * (1 + IIF(n > 1, (0.50/11.00) * (n - 1), 0))) AS price
INTO #tbl2 FROM numbers
;WITH numbers AS (
SELECT ROW_NUMBER() OVER (ORDER BY [value]) AS n
FROM string_split('1,2,3,4,5,6', ',')
)
SELECT n, (n * 20000 * (1 + IIF(n > 1, (0.50/5.00) * (n - 1), 0))) AS price
INTO #tbl3 FROM numbers
SELECT
#n_count = (tbl1.n + tbl2.n + tbl3.n),
#calculated = IIF(#n_count = 10, (tbl1.price + tbl2.price + tbl3.price), 0),
#tbl1n = IIF(#calculated > #last_found, tbl1.n, #tbl1n),
#tbl2n = IIF(#calculated > #last_found, tbl2.n, #tbl2n),
#tbl3n = IIF(#calculated > #last_found, tbl3.n, #tbl3n),
#last_found = IIF(#calculated > #last_found, #calculated, #last_found)
FROM #tbl1 tbl1
CROSS JOIN #tbl2 tbl2
CROSS JOIN #tbl3 tbl3
SELECT #last_found AS highest_value, #tbl1n AS tbl1n, #tbl2n AS tbl2n, #tbl3n AS tbl3n,
t1.price AS tbl1_price, t2.price AS tbl2_price, t3.price AS tbl3_price
FROM #tbl1 t1
INNER JOIN #tbl2 t2 ON t1.n = #tbl1n AND t2.n = #tbl2n
INNER JOIN #tbl3 t3 ON t3.n = #tbl3n
As can be seen, if the query finds a value higher than the previously found highest, it is storing the combination using multiple instances of #itemN = IIF(#calculated > #last_found, tbl.n, #itemN).
Is it possible to assign all #tblXn variables in one go? I could use a CONCAT, but I think it may slow down the query, as it is a string operation.
FYI - 'n' is a value between 0 and 20.

Answer 1

You can use apply :
SELECT n_count, calculated, last_found,
IIF(flag = 1, tbl1.n, #tbl1n) AS tbl1n,
IIF(flag = 1, tbl2.n, #tbl2n) AS tbl2n,
IIF(flag = 1, tbl3.n, #tbl3n) AS tbl3n
FROM tbl1 CROSS JOIN
tbl2 CROSS JOIN
tb CROSS APPLY
( VALUES (tbl1.n + tbl2.n + tbl3.n)
) t(n_count) CROSS APPLY
( VALUES (IIF(n_count = 10, ( (tbl1.n * tbl1.price), (tbl2.n * tbl2.price), (tbl3.n * tbl3.price) ), 0))
) tt(calculated) CROSS APPLY
( VALUES (IIF(calculated > #last_found, calculated, #last_found))
) lst(last_found) CROSS APPLY
( VALUES (IIF(calculated > last_found, 1, 0))
) cc(flag)
Note : You can further assign values to variable.

Answer 2

You shouldn't be using variables for this at all.
This would be much simpler written as below (without relying on undocumented/unguaranteed behaviour of assignment to variables across multiple rows)
SELECT TOP 1 CAST(combined_price AS DECIMAL(10, 2)) AS highest_value,
tbl1.n AS tbl1n,
tbl2.n AS tbl2n,
tbl3.n AS tbl3n,
tbl1.price AS tbl1_price,
tbl2.price AS tbl2_price,
tbl3.price AS tbl3_price
FROM #tbl1 tbl1
CROSS JOIN #tbl2 tbl2
CROSS JOIN #tbl3 tbl3
CROSS APPLY (VALUES (tbl1.price + tbl2.price + tbl3.price,
tbl1.n + tbl2.n + tbl3.n)) CA(combined_price, combined_n)
WHERE combined_n = 10
ORDER BY combined_price DESC