title: mysql python: check whether an input exists in database
body: <p>Can anyone help? 
     I have created a mysql database called 'ice cream' and connected it to python 3.3.5. I have a table with 2 columns : "MemberID" and "Username". Now i want to ask whether the user is a member or not, if he replies yes, my next question is ask him to key in his memberID, how do i check whether his input exists in the "MemberID" column my database, and if it exists, how can i print his "Username"?</p>
  
  <pre><code>conn = mysql.connector.connect(user='root', password='1234',
                                host='127.0.0.1',
                                database='icecream')
  
  cursor = conn.cursor
  
  Member_Ans=input("Are you a member? ")
  if Member_Ans=="yes":
  while True:     
      loginID=input("Please enter your member ID: ")
      # I don't know what code to type in this part...
  conn.close() 
  </code></pre>