i have a table, a drop down

lets assume you have the table named MyTable as (Column1, Column2, Column3)

you want to put Column1 values in dropdown, and show the Column2 and Column3 values related to selected Column1 value, is that right?

for that, assuming you know how to relate dropdown and table and put the Column1 value into dropdown's SelectedValue property, you can do as below, or better, use a StoredProcedure.

SqlCommand command = new SqlCommand()
{ 
   CommandText = string.Format("Select Column2, Column3 From MyTable Where Column1 = {0}", DropDown1.SelectedValue);
   Connection = new SqlConnection("Data Source=.;Initial Catalog={your database};Integrated Security=True");
   CommandType = CommandType.Text;
}

DataSet datasource = new DataSet();

using(SqlDataAdapter adapter = new SqlDataAdapter(command))
{
   adapter.Fill(datasource);
}

now use the datasource as you need, like :

GridView1.DataSoure = datasource.Tables[0];
GridView1.DataBind();

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Regards

H.Maadani