If you wanted too, you can make this follow the order of operations (except for parentheses) with a few small changes.

Where you currently have it decide which the last operator is by separately comparing each of the four operators, instead have it always pick addition and subtraction first, then the others. Your existing code to go from left to right will handle the rest.

--figure out which operation is last

if @addIdx > @firstIdx

begin

set @firstIdx = @addIdx

set @precedent = 1

end

if @subIdx > @firstIdx

begin

set @firstIdx = @subIdx

set @precedent = 1

end

--Add restriction that addition/subtraction must be found first (and so done last)

if @multIdx > @firstIdx AND @precedent = 0

begin

set @firstIdx = @multIdx

end

if @divIdx > @firstIdx AND @precedent = 0

begin

set @firstIdx = @divIdx

end

if @modIdx > @firstIdx AND @precedent = 0

begin

set @firstIdx = @modidx

end

Then in each of your cases, be sure to run the function on both halves

select @nopr2 = dbo.fn_simplemath(@opr2)

select @nopr1 = dbo.fn_simplemath(@opr1)