使用web服务使用jquery检查用户名或密码是真是假

这里是我的C#代码

public void Login(string kullaniciAd, string sifre)
    {
        try
        {
            SqlConnection conn = new SqlConnection("Data Source=.''SQLExpress; Initial Catalog=twitter;Integrated Security=SSPI");
            if (conn.State == ConnectionState.Closed)
                conn.Open();
            SqlCommand cmd = new SqlCommand("SELECT * FROM tblKullanici WHERE kullaniciAdi = @kullaniciAd or sifre = @kullaniciSifre", conn);
            cmd.CommandType = CommandType.Text;
            cmd.Connection = conn;
            cmd.Parameters.AddWithValue("@kullaniciAd", kullaniciAd);//username
            cmd.Parameters.AddWithValue("@kullaniciSifre", sifre);  //password
            cmd.ExecuteNonQuery();
            int UserExist = (int)cmd.ExecuteScalar();
            if (UserExist > 1)
            {
                //if given there is a user with given username and password?? 
                // i don't know how to do that first should i check username and then check that username's password or what?? 
                //successful
            }
            else
            {
                //wrong password or username
            }
            conn.Close();
        }
        catch (SoapException se)
        {
            throw se;
        }
    }

这是我的aspx页面

<script>
    $(document).ready(function () {
        $('#btnLogin').click(login);
    });
    function login() {
        var kullaniciAd = $('#userName').val();
        var sifre = $('#password').val();
        $.ajax({
            url: "http://localhost:63000/LoginService.asmx/Login",
            type: "POST", //or should it be GET? 
            dataType: "json",
            data: JSON.stringify({ kullaniciAd: kullaniciAd, sifre: sifre }),
            contentType: "application/json; charset=windows-1254",
            success: function () {
                alert("");// i have an alert div down there how can i show  if login is successful or not in that alert div
            },
            error: function (e) {
                alert(e.statusText);
            }
        })
    }
</script>
<%--<div class="alert alert-danger alert-dismissable">
        <button contenteditable="false" type="button" class="close" data-dismiss="alert"
              aria-hidden="true">
              ×</button>
              <strong>Well done!</strong>You successfully read this important alert message.
</div>--%>

这看起来很容易，但我无法决定我是在web服务中检查true还是false，只发送jquery一个数据（true，false），还是在jquery中通过调用true还是false的web方法来检查true或false？？