How to store math formula in SQL Server - sql-server

Question

I have a table contains the following data:
ID | expression
----|------------
1 | select 1+9
2 | select 6+23+3
----|------------
I need a query to get the result:
ID | expressionValue
----|------------
1 | 10
2 | 32
----|------------

Answer 1

You can try like this:
declare #x nvarchar(100)
select #x = expression from myTable where id = 1
EXECUTE sp_executesql #x
And if you want this to be done for all the rows of your table then try to create a cursor and execute it for your column like this:
DECLARE #myRes TABLE
(
ID INT ,
expression NVARCHAR(100)
)
DECLARE #temp TABLE ( ID INT )
DECLARE #ID INT ,
#expression NVARCHAR(100)
DECLARE cur CURSOR FAST_FORWARD READ_ONLY
FOR
SELECT ID , expression FROM myTable
OPEN cur
FETCH NEXT FROM cur INTO #ID, #expression
WHILE ##FETCH_STATUS = 0
BEGIN
DELETE FROM #temp
INSERT INTO #temp
EXEC ( #expression )
INSERT INTO #myRes
VALUES ( #ID, ( SELECT * FROM #temp ) )
FETCH NEXT FROM cur INTO #ID, #expression
END
CLOSE cur
DEALLOCATE cur
SELECT * FROM #myRes
Output:

Answer 2

If you got only + and - in formulas - then you can use XML.query:
SELECT ID,
CAST(
REPLACE(
REPLACE(
REPLACE(expression,'select ','<v><d>')
,'+','</d><d>')
,'-','</d><d>-') + '</d></v>'
as xml).query('for $s in /v return data(fn:sum($s/d))') as expressionValue
FROM YourTable
Output:
ID expressionValue
1 10
2 32
Also you can avoid using dynamic SQL to execute SELECT formula statements and use more secure way with XML.query:
CREATE TABLE #Results ( --Table to store results
ID int,
expressionValue nvarchar(max)
)
DECLARE #sql nvarchar(max) --will hold the dynamic SQL query
SELECT #sql = COALESCE(#sql,'DECLARE #x xml = ''''; INSERT INTO #Results ') +
'SELECT '+CAST(ID as nvarchar(max))+' as ID,
CAST(#x.query('''+REPLACE(expression,'select ','')+''') as nvarchar(max)) UNION '
FROM #YourTable --query generation
SELECT #sql = LEFT(#sql,LEN(#sql)-LEN(' UNION '))
If you make PRINT #sql you will get something like:
DECLARE #x xml = '';
INSERT INTO #Results
SELECT 1 as ID,
CAST(#x.query('1+9') as nvarchar(max))
UNION
SELECT 2 as ID,
CAST(#x.query('6+23+3') as nvarchar(max))
Then execute:
EXEC sp_executesql #sql
Then you can select from #Results table:
SELECT *
FROM #Results
Output:
ID expressionValue
1 10
2 32

Answer 3

Try this...
create table expr(id int,epres varchar(max))
insert into expr values(1,'select 2+2')
insert into expr values(2,'select 2-1')
declare #sql varchar(max),#id int
select top 1 #sql = epres,#id=id from expr where epres is not null order by id
while ##rowcount > 0
begin
exec(#sql)
select top 1 #sql = epres ,#id=id from expr where id > #id order by id;
end;