In order to divide two integer type fields in SQL Server you will have to apply a type cast before applying the mathematical operation.
Else you will receive zero (0) as a result whenever one of the numbers is not null, which is obviously not what we want.
SELECT (CAST(1 AS decimal) / CAST(2 AS decimal)) AS aNumber
This will work because at least one of the numbers is casted to decimal.
If you try to divide integer values the result will always be zero or NULL.
Dividing NULL by something will result in NULL. However I have not tried to divide a number by NULL so test before running into error.