SQL: Perform arithmetic operations on values in a column - sql

Question

I have a varchar that contains a formula:
declare #formula varchar(50) = 'X + Y + Z'
and I also have a table:
+---+---+
| A | B |
+---+---+
| X | 1 |
+---+---+
| Y | 2 |
+---+---+
| Z | 3 |
+---+---+
Column A values are unique and the formula may change. For example, if the formula is set to 'X + Y + Z' then the result would be 6. And if the formula is set to 'Z - X + Y' then the result is 4. Operations include only addition and subtraction. How can I achieve this? Having a hard time looking for where to start.

Answer 1

SQL Server does NOT support macro substitution, nor does it have an Eval()... this leaves Dynamic SQL
Example
Declare #YourTable Table ([A] varchar(50),[B] varchar(50))
Insert Into #YourTable Values
('X',1)
,('Y',2)
,('Z',3)
Declare #formula varchar(50) = 'X + Y + Z'
Select #formula=replace(#formula,[A],[B])
From #YourTable
Exec('Select NewValue='+#formula)
Returns
NewValue
6

Answer 2

Just for fun, here is a modified option which will support a TABLE
Example
Declare #YourValues Table ([A] varchar(50),[B] varchar(50))
Insert Into #YourValues Values
('X',1)
,('Y',2)
,('Z',3)
Declare #YourFormula Table (ID int,Formula varchar(50))
Insert Into #YourFormula Values
(1,'X + Y + Z'),
(2,'X - Y + Z')
Declare #SQL varchar(max) = stuff((Select concat(',(',ID,',',Formula,')') From #YourFormula For XML Path ('')),1,1,'')
Select #SQL=replace(#SQL,[A],[B])
From #YourValues
Create Table #TempResults (ID int,Calc money)
Exec('Insert Into #TempResults Select * from (values '+#SQL+')A(ID,Calc)')
Select * from #TempResults
Returns
ID Calc
1 6.00
2 2.00

Answer 3

This is rather crude and only works for +/- operands, however, I believe it satisfies the question.
DECLARE #Formulas TABLE (Formula NVARCHAR(MAX))
INSERT INTO #Formulas SELECT 'Z-X+Y'
DECLARE #Values TABLE(Name NVARCHAR(50), Value DECIMAL(18,2))
INSERT #Values VALUES ('X',1),('Y',2),('Z',3)
;WITH MySplitFormula AS
(
SELECT Value = SUBSTRING(Formula,Number,1) FROM #Formulas
CROSS APPLY (SELECT DISTINCT number FROM master..spt_values WHERE number > 0 AND number <= LEN(Formula))V
)
,NormalizedFormula AS
(
SELECT
DerivedOperations = CASE WHEN F.Value IN('+','-') THEN F.Value ELSE NULL END,
IsOperator = CASE WHEN F.Value IN('+','-') THEN 1 ELSE 0 END,
DerivedValues = CASE WHEN F.Value IN('+','-') THEN NULL ELSE V.Value END
FROM
MySplitFormula F
LEFT OUTER JOIN #Values V ON V.Name = F.Value
WHERE
NOT F.Value IS NULL
),
ValidatedFormula AS
(
SELECT DerivedOperations,DerivedValues FROM NormalizedFormula WHERE NOT((DerivedOperations IS NULL) AND (DerivedValues IS NULL))
),
Operators AS
(
SELECT
OrderIndex=ROW_NUMBER() OVER (ORDER BY (SELECT NULL)),
Operator=DerivedOperations FROM ValidatedFormula WHERE NOT DerivedOperations IS NULL
),
Operands AS
(
SELECT
OrderIndex=ROW_NUMBER() OVER (ORDER BY (SELECT NULL)),
Operand=DerivedValues FROM ValidatedFormula WHERE NOT DerivedValues IS NULL
)
,Marked AS
(
SELECT
OP.OrderIndex,
DoOperation = CASE WHEN OP.OrderIndex % 2 = 1 THEN 1 ELSE 0 END,
Operand1 = Operand,
Operator,
Operand2 = LEAD(Operand) OVER(ORDER BY OP.OrderIndex)
FROM
Operands OP
LEFT OUTER JOIN Operators OPR ON OPR.OrderIndex = OP.OrderIndex
)
,MarkedAgain AS
(
SELECT
*,
CalculatedValue = CASE WHEN DoOperation = 1 THEN
CASE
WHEN Operator = '+' THEN Operand1 + Operand2
WHEN Operator = '-' THEN Operand1 - Operand2
WHEN Operator IS NULL THEN
CASE WHEN LAG(Operator) OVER(ORDER BY OrderIndex) ='+' THEN Operand1 ELSE -Operand1 END
ELSE NULL
END
END
FROM
Marked
)
SELECT SUM(CalculatedValue) FROM MarkedAgain