String Expression to be evaluated to number
I don't think that is possible in a user defined function.
You could do it in a stored procedure, like:
declare @calc varchar(max)
set @calc = '10*4.5*0.5'
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
But dynamic SQL, like exec
or sp_executesql
, is not allowed in user defined functions.
Disclaimer: I'm the owner of the project Eval SQL.NET
For SQL 2012+, you can use Eval SQL.NET which can be run with SAFE Permission.
The performance is great (better than UDF) and honors operator precedence and parenthesis. In fact, almost all the C# language is supported.
You can also specify parameters to your formula.
-- SELECT 225.00
SELECT 10 * CAST(SQLNET::New('10*4.5*0.5').Eval() AS DECIMAL(18, 2))
-- SELECT 70
DECLARE @formula VARCHAR(50) = 'a+b*c'
SELECT 10 * SQLNET::New(@formula)
.Val('a', 1)
.Val('b', 2)
.Val('c', 3)
.EvalInt()