Question

Here is a broken down version of my problem :

I have a method. The argument is a list of integers. I wish to create an optimised SQL query that returns a particular value on all rows where the id of that row is equal to one of the integers in the argument list. Simple, right ?

I have a feeling I have made it more difficult than it needs to be :

private List<string> ReturnValue(List<int> ids)
        {
            List<string> ValuesIWantToReturn = new List<string>();
            StringBuilder sb = new StringBuilder("SELECT ValueIWantToReturnfrom table WHERE ");
            foreach (int id in ids)
            {
                sb.Append( string.Format("ID = {0} OR ", id) );
            }
            sb.Remove(sb.Length - 3, 3); //remove trailing "OR"
                           sb.Append(";");
            SqlDataReader reader =  RunSelectQuery( sb.ToString() );
            while (reader.Read())
            {
                ValuesIWantToReturn.Add(reader.GetString(0));
            }

            return ValuesIWantToReturn;
        }

Any feedback on the general readability and structure of my code would be appreciated too. It’s always nice to improve 🙂

Answer 1

You can use the IN syntax rather than OR

 WHERE id IN (1,2,3,4)

It may be more efficient to pass the list of IDs as a table valued parameter to a stored procedure, and then join that to your table, but that may be over engineering the solution – depending on how long your list of numbers is.

Instead of your loop, you can use string.Join to build your list

string query = "SELECT ValueIWantToReturn from table WHERE ID IN ("
    + string.Join(",", ids)
    + ")";

(assuming that there is always at least one number in the list)