无法将值从下拉列表选定的值传递给 SQL WHERE 子句

Question

I am trying to pass value from dropdown list to sql query WHERE clause but it is failing and not returning any value but when i give the value directly in WHERE it is working fine only problem is from addwithvalue command it is not passing the value. When i run this it is showing as there is no value at position 0 in line ' string champ = dt.Rows[0]["mc"].ToString(); ' Please check and help,

            string query = "SELECT mc, tower, image from datatable WHERE month= '@month' AND mc IS NOT NULL AND image IS NOT NULL";
            SqlCommand cmd = new SqlCommand(query, con);
            cmd.Parameters.AddWithValue("@month", ChampMonth.SelectedValue);
            SqlDataAdapter sda = new SqlDataAdapter(cmd);
            cmd.ExecuteScalar();
            DataTable dt = new DataTable();
            sda.Fill(dt);
            string champ = dt.Rows[0]["mc"].ToString();
            string tower = dt.Rows[0]["tower"].ToString();
            string img = dt.Rows[0]["image"].ToString();
            Label1.Text = champ;
            Label2.Text = tower;
            img = Server.MapPath(img);
            Image1.ImageUrl = img;
        }

Answer 1

You code can look like this:

        string query = "SELECT mc, tower, image from datatable WHERE month = @month " +
                       "AND mc IS NOT NULL AND image IS NOT NULL";

        using (SqlCommand cmd = new SqlCommand(query, con))
        {
            cmd.Connection.Open();

            cmd.Parameters.Add("@month", SqlDbType.NVarChar).Value = ChampMonth.SelectedValue;

            DataTable dt = new DataTable();
            dt.Load(cmd.ExecuteReader());

            if (dt.Rows.Count > 0) {
                Label1.Text = dt.Rows[0]["mc"].ToString();
                Label2.Text = dt.Rows[0]["tower"].ToString();
                string img = Server.MapPath(dt.Rows[0]["image"].ToString());
                Image1.ImageUrl = img;
            }
        }

a few things:

The sql command object has a connection object - no need to create one
The sql command object has a reader built in - no need to create one
The sql command object has a command text.

You ONLY ever need a data adaptor if you going to update your data table object in code.

And you don't show how/when you created your connection object.

You should post the markup that drives the dropdownlist (combo box), since it not clear if it returns 1-12, or actual text - that part might still be wrong.