Use this function to your required event
private void loadData()
{
SqlCommand cmd = default(SqlCommand);
SqlConnection con = default(SqlConnection);
con = new SqlConnection("<your connection="" string="" here=""></your>");
con.Open();
cmd = new SqlCommand("<your query="" here=""></your>", con);
SqlDataReader reader = cmd.ExecuteReader();
TestBox1.Text = Convert.ToString(reader["<column name="" here=""></column>"]);
con.Close();
}