SQL Server : converting varchar to INT

Question

I am stuck on converting a varchar column UserID to INT. I know, please don\'t ask why this UserID column was not created as

Answer 1

This question has got 91,000 views so perhaps many people are looking for a more generic solution to the issue in the title "error converting varchar to INT"

If you are on SQL Server 2012+ one way of handling this invalid data is to use TRY_CAST

SELECT TRY_CAST (userID AS INT)
FROM   audit 

On previous versions you could use

SELECT CASE
         WHEN ISNUMERIC(RTRIM(userID) + '.0e0') = 1
              AND LEN(userID) <= 11
           THEN CAST(userID AS INT)
       END
FROM   audit 

Both return NULL if the value cannot be cast.

In the specific case that you have in your question with known bad values I would use the following however.

CAST(REPLACE(userID COLLATE Latin1_General_Bin, CHAR(0),'') AS INT)

Trying to replace the null character is often problematic except if using a binary collation.