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

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.

Solution: where some_column NOT LIKE '%[^0-9]%' Is correct.

Just one important note: Add validation for when the string column = '' (empty string). This scenario will return that '' is a valid number as well.

Use Not Like

where some_column NOT LIKE '%[^0-9]%'

Demo

declare @str varchar(50)='50'--'asdarew345'

select 1 where @str NOT LIKE '%[^0-9]%'