sql即使分配时为null也不会返回值

Question

Using asp.net, C#, SQL Server 2008.

Scenario: User attempts to log into web app. App checks username against list to get UserID . If this user is a known user, page opens fine. If user is not a known user, it SHOULD open to page with notice to contact admin.

I have been unable to write the SQL stored procedure so that it will return a value of 0 (or anything else for that matter) so it can be used to trigger controls. I've executed the SQL as a test, and it works; but it errors out every time on the asp side.

Any and all assistance is greatly appreciated!

SQL Server stored procedure code:

ALTER PROCEDURE [dbo].[spGetUserID]
-- Add the parameters for the stored procedure here
   (@Username as varchar(64))
AS
BEGIN
  SET NOCOUNT ON;

  DECLARE @X  INT

  SET @X = (SELECT COUNT(*) FROM Users WHERE (Username = @Username))

  If @X > 0
     RETURN 
        (SELECT UID FROM Users WHERE (UserName = @Username))
  ELSE
     RETURN 99999  --IVE ALSO TRIED USING 0 HERE. 
END

ASP.NET stored procedure call

 public int GetUserID(string Username)
 { 
       try
       {
            SQLCON = new SqlConnection(connectionString);
            SQLCON.Open();
            SQLCmd = new SqlCommand("spGetUserID", SQLCON);
            SQLCmd.CommandType = CommandType.StoredProcedure;
            SQLCmd.Parameters.Add("@username", SqlDbType.VarChar).Value = Username;
            int userID = (Int32)SQLCmd.ExecuteScalar();
            return userID;  //THIS ALWAYS JUMPS TO EXCEPTION
        }
        catch
        {
            return 0;
        }
        finally
        {
            SQLCON.Close();
        }
    }

Answer 1

ExecuteScalar() is meant for a query that returns one row with one column.

To get the return value of a stored procedure, use a parameter with direction ReturnValue :

sqlcomm.Parameters.Add("@retVal", SqlDbType.Int).Direction = 
    ParameterDirection.ReturnValue;
SQLCmd.ExecuteNonQuery();
var result = (int) sqlcomm.Parameters["@retVal"].Value;

Answer 2

Try unwrapping your select statement. The ExecuteScalar command retrieves the first column of the first row in the result set, or a null reference if the result set is empty. Your stored proc doesn't actually return a result set. Try...

ALTER PROCEDURE [dbo].[spGetUserID]
-- Add the parameters for the stored procedure here
   (@Username as varchar(64))
AS
BEGIN
  If Exists(SELECT 1 FROM Users WHERE (Username = @Username))
     SELECT UID FROM Users WHERE (UserName = @Username)
  ELSE
     SELECT 99999
END