How do I fix my error on my DropDownList?

See more:

C#

ASP.NET

Javascript

WebForms

, +

I'm a beginner so please bear with me...

I already have a table with these columns
-ID (for primary key purposes)
-region (equivalent to a state in other countries)
-city (within the region or state)

What I want to happen is this, whenever I change DropDownListRegion, I want to have the DropDownListCity populated with only the cities inside that region.

Here's my code:

string regionvar = ""; //to be used on ***

        protected void Page_Load(object sender, EventArgs e)
        {
            if (Page.IsPostBack)
            {
                
            }
            else
            {
                selectData();
            }
        }

        protected void selectData()
        {
            string myConnectionString = "server=localhost;uid=root;" + "pwd=xxxxx;database=xxxxx;";
            MySql.Data.MySqlClient.MySqlConnection conn = new MySql.Data.MySqlClient.MySqlConnection(myConnectionString);

            DataTable dt = new DataTable();

            string commandText = "select * from table";

            using (MySqlConnection openconn = conn)
            using (MySqlDataAdapter adap = new MySqlDataAdapter(commandText, openconn))
            {
                adap.Fill(dt);
                GridViewUserInfoTable.DataSource = dt;
                GridViewUserInfoTable.DataBind();
            }

            MySql.Data.MySqlClient.MySqlConnection conn1 = new MySql.Data.MySqlClient.MySqlConnection(myConnectionString);

            DataTable dt1 = new DataTable();

            string commandText1 = "select distinct region from REGIONS order by ID";

            using (MySqlConnection openconn1 = conn1)
            using (MySqlDataAdapter adap1 = new MySqlDataAdapter(commandText1, openconn1))
            {
                adap1.Fill(dt1);
                if (dt1.Rows.Count > 0)
                {
                    DropDownListRegion.DataSource = dt1;
                    DropDownListRegion.DataTextField = "region";
                    DropDownListRegion.DataValueField = "region";
                    DropDownListRegion.DataBind();
                    regionvar = DropDownListRegion.SelectedItem.Text; //setting value for ***
                }
                
            }

            MySql.Data.MySqlClient.MySqlConnection conn2 = new MySql.Data.MySqlClient.MySqlConnection(myConnectionString);

            DataTable dt2 = new DataTable();

            string commandText2 = "select city from REGIONS order by city where region = " + regionvar; //using value of ***

            using (MySqlConnection openconn2 = conn2)
            using (MySqlDataAdapter adap2 = new MySqlDataAdapter(commandText2, openconn2))
            {
                adap2.Fill(dt2);
                if (dt2.Rows.Count > 0)
                {
                    DropDownListCity.DataSource = dt2;
                    DropDownListCity.DataTextField = "city";
                    DropDownListCity.DataValueField = "city";
                    DropDownListCity.DataBind();
                }
            }
            
        }

I'm getting the error somewhere in where region = "RegionName"

Any suggestions will be highly appreciated. Thank you very much!

---
After solution number1:
okay, so i did this

string commandText2 = "select city from REGIONS where region=" + regionvar + " order by city";

a new error appears:
Unknown column 'REGIONNAME' in 'where clause'

---
After solution number 2 and 3:
so I made this:

<asp:DropDownList ID="DropDownListRegion" runat="server" AutoPostBack="True" onselectedindexchanged="DropDownListRegion_SelectedIndexChanged">
        </asp:DropDownList>

protected void DropDownListRegion_SelectedIndexChanged(object sender, EventArgs e)
        {
            DropDownListCity.Enabled = true;
            regionvar = DropDownListCity.SelectedItem.Text; //ERROR HERE
            
            string myConnectionString = "server=localhost;uid=root;" + "pwd=XXXXX;database=XXXXX;";
            MySql.Data.MySqlClient.MySqlConnection conn2 = new MySql.Data.MySqlClient.MySqlConnection(myConnectionString);

            DataTable dt2 = new DataTable();

            string commandText2 = "select city from REGIONS where region=" + regionvar + " order by city";

            using (MySqlConnection openconn2 = conn2)
            using (MySqlDataAdapter adap2 = new MySqlDataAdapter(commandText2, openconn2))
            {
                adap2.Fill(dt2);
                if (dt2.Rows.Count > 0)
                {
                    DropDownListCity.DataSource = dt2;
                    DropDownListCity.DataTextField = "city";
                    DropDownListCity.DataValueField = "city";
                    DropDownListCity.DataBind();
                }
            }

            if (Page.IsPostBack == true)
            {

            }
        }

I get an error on this line saying: Object reference not set to an instance of an object.
regionvar = DropDownListCity.SelectedItem.Text;