Question

i keep getting this error, i dont know why, im still new to c#. kindly help me figure this out please. i have two dropdownlist that would populate data based on first dropdownlist selected value.

when i select a value on the first dropdownlist, i get that error..

here is my code..

protected void Page_Load(object sender, EventArgs e)
    {
        if (!IsPostBack)
        {
            //read sql server connection string from web.config file
            string constring = ConfigurationManager.ConnectionStrings["AccreString"].ConnectionString;
            SqlConnection conn = new SqlConnection(constring);
            DataTable dt = new DataTable("emed_province");

            using (conn)
            {
                conn.Open();
                SqlCommand comm = new SqlCommand("SELECT *  FROM emed_province ORDER BY PROVINCE_NAME ASC", conn);
                SqlDataAdapter adptr = new SqlDataAdapter(comm);
                adptr.Fill(dt);
            }

            ddlProvince.DataSource = dt;
            ddlProvince.DataTextField = "PROVINCE_NAME";
            ddlProvince.DataValueField = "PROVINCE_CODE";
            ddlProvince.DataBind();
        }
    }

    protected void ddlProvince_SelectedIndexChanged(object sender, EventArgs e)
    {
        string constring = ConfigurationManager.ConnectionStrings["AccreString"].ConnectionString;
        SqlConnection conn = new SqlConnection(constring);
        DataTable dt = new DataTable("emed_province");

        using (conn)
        {
            conn.Open();
            SqlCommand comm = new SqlCommand("SELECT CITY_NAME FROM emed_city WHERE PROVINCE_CODE ="+ddlProvince.SelectedValue, conn);
            SqlDataAdapter adptr = new SqlDataAdapter(comm);
            adptr.Fill(dt);
        }

        ddlCity.DataSource = dt;
        ddlCity.DataTextField = "CITY_NAME";
        ddlCity.DataValueField = "CITY_CODE";
        ddlProvince.DataBind();
    }
}

Answer 1

It happens because you passed the raw value without quotes, so the database thought you mean field name.

Avoid this all mess by using Parameters:

using (conn)
{
    conn.Open();
    SqlCommand comm = new SqlCommand("SELECT CITY_NAME FROM emed_city WHERE PROVINCE_CODE=@pcode", conn);
    comm.Parameters.AddWithValue("@pcode", ddlProvince.SelectedValue);
    SqlDataAdapter adptr = new SqlDataAdapter(comm);
    adptr.Fill(dt);
}