Question

I’m trying to randomly select a card from a table of cards with columns c_value and c_suit using a procedure. After selecting it, the procedure should update that entry’s taken field to be ‘Y’.

create or replace procedure j_prc_sel_card(p_value OUT number,
                                           p_suit OUT number)
AS

   CURSOR CUR_GET_RAND_CARD IS SELECT c_value, 
                                      c_suit
                                 FROM (SELECT c_value, 
                                              c_suit, 
                                              taken
                                         FROM jackson_card
                                     ORDER BY dbms_random.value)
                                WHERE rownum = 1
                        FOR UPDATE OF taken;

BEGIN

  OPEN CUR_GET_RAND_CARD;
  FETCH CUR_GET_RAND_CARD into p_value, p_suit;

  UPDATE jackson_card 
     SET taken = 'Y' 
   WHERE c_value = p_value 
     AND c_suit = p_suit;

  CLOSE CUR_GET_RAND_CARD;

END;

Then I am trying to get the selected card and output what it is as a start. With this:

SET serveroutput on;

DECLARE v_value number;
        v_suit number;

BEGIN

  j_prc_sel_card(p_value => v_value,p_suit => v_suit);
  DBMS_OUTPUT.PUT_LINE(v_value);
  DBMS_OUTPUT.PUT_LINE(v_suit);

END;
/

However i got the error stated in the title and it seems my way of selecting a random card is stopping me from doing an update. Thanks in advance!

Answer 1

Here is a different take on the scenario (I did also address your immediate problem in a different answer).

Given that we really are building a card-dealing program (as opposed to working with a test case for a business scenario) I didn’t like the TAKEN column. Updating a table column to mark a transitory state seems wrong. What happens when we want to play another game?

The following solution resolves this by populating an array with all the cards in a random order upfront (the shuffle). The cards are dealt by simply taking the next entry off the stack. The package offers a choice of approach for running out of cards: either throw a user-defined exception or just cycle through the deck again.

create or replace package card_deck is

    no_more_cards exception;
    pragma exception_init(no_more_cards, -20000);

    procedure shuffle;

    function deal_one 
        ( p_yn_continuous in varchar2 := 'N')
        return cards%rowtype;

end card_deck;
/

create or replace package body card_deck is

    type deck_t is table of cards%rowtype;
    the_deck deck_t;

    card_counter pls_integer;

    procedure shuffle is
    begin
        dbms_random.seed (to_number(to_char(sysdate, 'sssss')));
        select *
        bulk collect into the_deck
        from cards
        order by dbms_random.value;
        card_counter := 0;
    end shuffle;

    function deal_one
        ( p_yn_continuous in varchar2 := 'N')
        return cards%rowtype
    is
    begin
        card_counter := card_counter + 1;
        if card_counter > the_deck.count() 
        then
            if p_yn_continuous = 'N'
            then
                raise no_more_cards;
            else
                card_counter := 1;
            end if;
        end if;
        return the_deck(card_counter);
    end deal_one;

end card_deck;
/

Here it is in action. Don’t use an open LOOP if you set the continuous dealing mode to Y.

SQL> set serveroutput on
SQL>
SQL> declare
  2      my_card cards%rowtype;
  3  begin
  4      card_deck.shuffle;
  5      loop
  6          my_card := card_deck.deal_one;
  7          dbms_output.put_line ('my card is '||my_card.c_suit||my_card.c_value);
  8      end loop;
  9  exception
 10      when card_deck.no_more_cards then
 11          dbms_output.put_line('no more cards!');
 12  end;
 13  /
my card is HA
my card is H7
my card is DJ
my card is CQ
my card is D9
my card is SK
no more cards!

PL/SQL procedure successfully completed.

SQL>

You may think I’m not dealing with a full deck. You wouldn’t be the first to think that 😉