c# making combobox filter for sql columns

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C#

SQL

combobox

Hey,
I'm trying to use 2 comboboxes that all reads data from different sql table. I need to do that;
-When i select something on combobox1 (it only reads names on a Column)
-when i want to select something on combobox 2(it only reads Surnames on a Column in different table), i want to see names that starts with name on combobox1.



here is my code;

SqlConnection con1 = new SqlConnection("Data Source=.;Initial Catalog=AY_DB;Integrated Security=True");
con1.Open();
SqlCommand cmd2 = new SqlCommand("select Name from CLASS", con1);
SqlCommand cmd3 = new SqlCommand("select Surname from CLASS2 where (Name = '" + comboBox1.Text + "')", con1);
SqlDataReader dr1,dr2;

try
{
    dr1 = cmd2.ExecuteReader();

    while (dr1.Read())
    {

        comboBox1.Items.Add(dr1["Name"]);

    }
    con1.Close();

}
catch (Exception es)
{
    MessageBox.Show(es.Message, "FAIL");
}
try
{
    con1.Open();
    dr5 = cmd3.ExecuteReader();
    while(dr2.Read())
    {
        comboBox2.Items.Add(dr5["Surname"]);
    }
    con1.Close();
}

    catch(Exception eg)
{
        MessageBox.Show(eg.Message,"FAIL");

    }

Names in CLASS table is as same as in CLASS2 table and their table names are same too(both column names are "name"). I can see names on combobox1. It's ok but, after selecting an item on combobox1, i couldn't see an item on combobox2. It seems empty.
How can i see surnames which starts with item on combobox1?