In connectStr, pass your Connection String.
string connectStr = "";
string updateQuery = "UPDATE T1
SET T1.name = T2.name, T1.address_ = T2.address_
FROM TABLE1 T1
INNER JOIN TABLE2 T2
ON T1.billNo = T2.billNo
WHERE T2.billNo LIKE 'A100%'";
SqlConnection conn = new SqlConnection(connectStr);
SqlCommand cmd = new SqlCommand(updateQuery,conn);
conn.Open();
int result = cmd.ExecuteNonQuery();
conn.Close();
if(result>0)
{
ClientScript.RegisterClientScriptBlock(this.GetType(), "alertbox", "<script language='javascript'>alert('Updated');</script>");
}
Hope this solves your problem!! :)