Проблема подключения, когда emailid существует в базе данных или нет?

---

Issue With Connection When Working With SSMS.

How to Check EmailId Exist in the database or not?

<pre><pre>
        protected void Button1_Click(object sender, EventArgs e)
        {
            string firstname = txtFirstName.Text;
            string lastname = txtLastName.Text;
            string emailid = txtEmailId.Text;
            string password = txtclientpassword.Text;
            Registration_Click(firstname, lastname, emailid, password);
        }

 void Registration_Click(string firstname,string lastname,string emailid,string Password)
        {
            string conn = ConfigurationManager.ConnectionStrings["connstr"].ToString();
            SqlConnection cn = new SqlConnection(conn);

            cn.Open();

            string Insertquery = "Insert into tbladminclient(FirstName,LastName,EmailId,Password) values(@FirstName,@LastName,@EmailId,@Password)";
            SqlCommand cmd = new SqlCommand(Insertquery, cn);
            cmd.CommandType = CommandType.Text;

            string query = "SELECT * FROM tbladminclient WHERE EmailId='" + txtEmailId.Text + "'";
            cmd.Parameters.AddWithValue(query, cn);
            int count = (int)cmd.ExecuteScalar();

            if (count > 0)
            {
                Label2.Text = "EmailId is Already In Use";
            }

            cmd.Parameters.AddWithValue("@FirstName", firstname);
            cmd.Parameters.AddWithValue("@LastName", lastname);
            cmd.Parameters.AddWithValue("@EmailId", emailid);
            cmd.Parameters.AddWithValue("@Password", Password);

            try
            {
                int validateOperation = cmd.ExecuteNonQuery();
                if (validateOperation > 0)
                {
                    Response.Write("successfully Registration");
                    Response.Redirect("ClientLogin.aspx");
                }
                else
                {
                    Response.Write("Not successfully Registration");
                }
            }
            catch (SqlException e)
            {
                Response.Write("error");
            }
            finally
            {
                cn.Close();
            }
        }
    }

Как определить, существует ли Emailid в базе данных или нет??



Изображение:

Error:
<a href="https://imgur.com/a/hzILnC1">Imgur: The magic of the Internet</a>[<a href="https://imgur.com/a/hzILnC1" target="_blank" title="New Window">^</a>]

Что я уже пробовал:

I want the Emailid is already is inserted in the database then not inserted the second time?

---