Advised to use parameterized query always. Showing example how to fill combo box(I assume klient is table name).
SqlCommand novyprikaz = new SqlCommand("SELECT * FROM klient WHERE akce=@xyz", spojeni);
spojeni.Open();
cmd.Parameters.AddWithValue("xyz",your actual value);
SqlDataAdapter da = new SqlDataAdapter(novyprikaz);
DataSet ds = new DataSet();
da.Fill(ds);
comboBox2.DataSource=ds;
comboBox2.DataBind();
Regards.. :laugh: