SQL Server : How to test if a string has only digit characters

Question

I am working in SQL Server 2008. I am trying to test whether a string (varchar) has only digit characters (0-9). I know that the IS_NUMERIC function can give spurious results.

Answer 1

There is a system function called ISNUMERIC for SQL 2008 and up. An example:

SELECT myCol
FROM mTable
WHERE ISNUMERIC(myCol)<> 1;

I did a couple of quick tests and also looked further into the docs:

ISNUMERIC returns 1 when the input expression evaluates to a valid numeric data type; otherwise it returns 0.

Which means it is fairly predictable for example

-9879210433 would pass but 987921-0433 does not. $9879210433 would pass but 9879210$433 does not.

So using this information you can weed out based on the list of valid currency symbols and + & - characters.