Conversion failed when converting the varchar value '1,' to data type int

Question

I have table categories (c) and an another table (x) with a column which can contain cat IDs separated with comma as varchar data type. I want to Select related categories but I'm having error "Conversion failed when converting the varchar value '5,' to data type int." when trying to select:

SELECT ID, Title FROM c WHERE ID IN (SELECT catIDs FROM x WHERE ID=any);

The subquery returns data like "1,3,4"

Solution 1

You need to split the 1,3,4 string returned by the subquery into separate int values. SQL Server does not have a built-in function to do it, but you can use this user-defined function.

Create the function dbo.Split in your database and then re-write your query as follows:

SELECT ID, Title
FROM c
WHERE ID IN
  (
    SELECT s
    FROM dbo.Split(',', '1,3,4')
  )

I replaced the subquery with example results 1,3,4 to shorten the query and make it easier to understand.

Solution 2

If I get it right, you actually have values like "1,3,4" in your column catIDs. So you should extract a substring in the select of your subquery.

By the way, I'm not an MS SQL Server expert, but it's probably a bad database design to do so. I'm not sure the RDBMS engine will use indexes in such a case...