Evaluate expression stored in Varchar Column directly in the "select" statement - sql

Question

I have a table named PriceDetails with three columns
"price","discount formula" and "finalprice". I have to calculate final price based on "Price" and "discount formula" columns.
My table looks like this,
Price DiscountFormulae
100 100*(3/100)
200 200*(1.1/100)+200*(5/100)
300 300*(1/100)+300*(3/100)+300*(2/100)
400 400*(7/100)+400*(6.6/100)+400*(5.5/100)+400*(4/100)
I want to calculate final price. The formula would be "Price"-"DiscountFormulae"
for example
100 - (100*(3/100)) =97
My Expected Output would be
Price DiscountFormulae FinalPrice
100 100*(3/100) 97
Note: My DiscountFormulae Column is Varchar(1000)
How do I get this. Please help me.

Answer 1

Not very good solution, but it shows, how difficult is it:
CREATE TABLE #temp (Price int, DiscountFormula Varchar(1000))
INSERT INTO #temp
(#temp.Price, #temp.DiscountFormula)
VALUES
(100,'100.0*(3.0/100)'),
(200,'200.0*(1.1/100)+200*(5.0/100)'),
(300,'300.0*(1.0/100)+300*(3.0/100)+300*(2.0/100)'),
(400,'400.0*(7.0/100)+400*(6.6/100)+400*(5.5/100)+400*(4.0/100)')
DECLARE #price int
DECLARE cur CURSOR FOR SELECT t.Price FROM #temp AS t
OPEN cur
FETCH NEXT FROM cur INTO #price
WHILE (##FETCH_STATUS = 0)
BEGIN
DECLARE #sql nvarchar(MAX) = N'
SELECT
t.Price,
t.DiscountFormula,
' + (SELECT TOP 1 DiscountFormula FROM #Temp WHERE Price = #price) + N' as Value
FROM #temp AS t
WHERE Price = ' +CONVERT(nvarchar(max),#price)
EXEC sp_executesql #sql
FETCH NEXT FROM cur INTO #price
END
CLOSE cur
DROP TABLE #temp
By the way, use float values in formula.

Answer 2

You could do it in a stored procedure, like:
But dynamic SQL, like exec or sp_executesql, is not allowed in user defined functions.
DECLARE #calc varchar(max)
SET #calc = '100*(3/100)'
DECLARE #sql nvarchar(max)
DECLARE #result float
SET #sql = N'SET #result = ' + #calc
exec sp_executesql #sql, N'#result float output', #result out
SELECT #result