title: Sql multiple reservations and duplicate vallues
body: <p>Lets assume that we have a table named <code>Reserations( PK, clientID, ORDER_NUMBER, CREDIT_CARD )</code>. A client can make multiple reservations but a reservation is considered complete when <code>CREDIT_CARD</code> is not null ( meaning that the client has prepaid the order ) visa, mastercard,etc.. </p>
  
  <p>So we have this table full of reservations and I want to clean it up by the following rules: if a client has made a valid reservation ( credit card is not NULL ) then if this client has other reservations that are not paid ( the credit card is null ) I will auto reserve them for him( meaning that I will add the credit card type in the <code>CREDIT_CARD</code> columns that are null for this specific client ). Otherwise the client is not valid( not a single valid credit card ) his records will be deleted. </p>
  
  <p>How do I implement this in SQL microsoft access? My thoughts are : 
  select the table, remove the duplicates and update the records. The only problem here is how do I know if there is at least one valid reservation made? Maybe use a count function to count the valid reservations for each client ?</p>