Logical Error in my application sql statement
<p>My application except patientNumber then poplate the dropdown for the visits with the VisitNumbers.A VisitNumber is generate for the patient for every visit.
when i click the search button the get the visitNumber for the patient and populate the Dropdownlist i get and error:</p>

<pre><code>Line 35:                 {
Line 36:                     con.Open();
Line 37:                     SqlDataReader reader = cmd.ExecuteReader();
Line 38:                     
Line 39:                     reader = cmd.ExecuteReader();



Stack Trace:


[SqlException (0x80131904): Incorrect syntax near '.'.
Incorrect syntax near 'a'.]
System.Data.SqlClient.SqlConnection.OnError(SqlException exception, Boolean  breakConnection, Action`1 wrapCloseInAction) +1753346

HERE IS MY CODE:

 public List&lt;string&gt; Get_VisitNumber()
    {
        List&lt;string&gt; visitnum = new List&lt;string&gt;();
        string patient_number = txtPatientNumber.Text;

        string connect =       
 System.Configuration.ConfigurationManager.ConnectionStrings["db_connection"].ToString();
        SqlConnection con = new SqlConnection(connect);
        string select_statement = "SELECT Visit_Number FROM Patient a ,Visit b"
          + "WHERE a.Patient_Number=b.Patient_Number";


        SqlCommand cmd = new SqlCommand(select_statement, con);


        cmd.Parameters.AddWithValue("@b.Patient_Number", patient_number);

        using (con)
        {
            con.Open();
            SqlDataReader reader = cmd.ExecuteReader();

            reader = cmd.ExecuteReader();
            while (reader.Read())
            {
                if (reader["Patient_Number"] != DBNull.Value)
                {
                    string VID = reader["Visit_Number"].ToString();
                    visitnum.Add(VID);
                }
                else
                {
                    Response.Write("&lt;script language=javascript&gt;alert('Patient Number not Found.');&lt;/script&gt;");

                }


            }//   end while





        } // end using 

        return visitnum;
    }





    protected void btn_search_Click(object sender, EventArgs e)
    {
        DropDownList1.DataSource = Get_VisitNumber();

        DropDownList1.DataBind();
    }
</code></pre>
