Showing posts from January, 2017

SQL ISNUMERIC() function

Imagine you have a column of data which is supposed to contain numbers, but you don't know which ones are numbers. Imaging you also live in a world where SQL Server 2012 and above don't exist. Now imagine you stumble across the function ISNUMERIC one day and think to yourself "huzzah! My worries are over!". Now imagine you put that check in to your code, push it to production, and low and behold, it doesn't do what you expect.

This is documented elsewhere as well but ISNUMERIC might not do what you expect. It includes characters which aren't strictly speaking numeric values. For instance, it contains several currency signs. It allows some white space characters, and it allows commas, pluses, minuses and more. Consider the following.

select Idx = num, Chr = char(num), IsNum = isnumeric(char(num)), IsNum_e0 = isnumeric(char(num) + 'e0') from (select top 255 num = row_number() over (order by (select null)) from sys.all_objects) a or…