MySQL - INSERTAR múltiples valores condicionalmente

Ok, so I have a table which holds bets on games.
The table holds the columns: user_id, event_id, bet.
A user can send his/her (multiple) bets to the server in one request.

  • I need to insert multiple bets using one query, while checking that none of the bets are on an event that already started/finished.
  • In case of at least 1 started/finished event, I don't really care if the whole query cancels, or just ignores the 'unqualified' bets.

Pregunta
How can I insert multiple bets (rows) with one query, while conditioning the insert on a select statement (which checks for each of the events' statuses)?

Here is the query I would've used if it worked (and it doesn't of course): 

INSERT INTO bet_on_event (user_id, event_id, bet)
VALUES (1,5,1), (1,6,2)
IF (SELECT COUNT(*) FROM events WHERE _id IN(5,6) AND status=0) = ?;

Explicación
1. As mentioned, the values are pre-made - requested by the user.
2. Games/events have status. 0 means a game hasn't started, so it's ok to bet.
3. The select statement just counts how many of the requested events have status 0.
4. The 'IF' should check if the count from (3) equals the number of events the user requested to bet on, thus confirming that all the events are ok to bet on.

The 'IF' should be replaced with something that work, and the whole statement can be replaced if you have a better idea for what I'm trying to achieve.

A simpler query (which isn't enough for my case, but works with 1 row) is: 

INSERT INTO bet_on_event (user_id, event_id, bet)
SELECT 1,5,1 FROM dual
WHERE (SELECT COUNT(*) FROM events WHERE _id IN(5,6) AND status=0) = ?;

Any idea? Is this even possible? Betting is gonna be used a lot, so I want to do it as quick as possible - with 1 query.
Muchas gracias.

EDITAR
That is what I ended up doing, taken from Thorsten's answer (I changed it to a dynamically built query, as that is what I need):

var query='INSERT INTO bet_on_event (user_id, event_id, bet)';

    for(var i=0; i<eventIds.length; i++){
    query+= ' SELECT ' + userId + ',' + eventIds[i] + ',' + bets[i] 
       + ' FROM dual WHERE EXISTS (SELECT * FROM events WHERE id = ' + eventIds[i]
       + ' AND Status = 0)';
        if(i < eventIds.length - 1){  
             query += ' UNION ALL';
        }
    }

Where eventIds and bets are in a corresponding order (like a map)

EDIT 2
I also wanted to UPDATE the bets which already exist (in case the user wanted to...). So there's a need to update each row with the relevant bet in the array. This is the solution: 

ON DUPLICATE KEY UPDATE bet=VALUES(bet)

Just added (concatenated) to the end of the query...

preguntado el 28 de mayo de 14 a las 11:05

2 Respuestas

Does this work for you? It inserts 1,5,1 if there is no event for id 5 that has started. Same for 1,6,1 and id 6.

INSERT INTO bet_on_event (user_id, event_id, bet)
SELECT 1,5,1 FROM dual WHERE NOT EXISTS 
  (SELECT * FROM events WHERE _id = 5 AND Status <> 0)
UNION ALL
SELECT 1,6,1 FROM dual WHERE NOT EXISTS 
  (SELECT * FROM events WHERE _id = 6 AND Status <> 0);

EDIT: If you don't want to insert anything in case one or more of the games have started, you can simply replace WHERE _id = 5 e WHERE _id = 6 WHERE _id IN (5,6). Or have just one exists clause:

INSERT INTO bet_on_event (user_id, event_id, bet)
SELECT *
FROM
(
  SELECT 1,5,1 FROM dual
  UNION ALL
  SELECT 1,6,1 FROM dual
) tmp
WHERE NOT EXISTS (SELECT * FROM events WHERE _id IN (5,6) AND Status <> 0);

contestado el 28 de mayo de 14 a las 15:05

thx for the reply. Wouldn't this query be slow? A user can be on many events at once.. I'm checking if it's working right now.. - chico_m

This shouldn't be slow provided there is an index on _id. The real question is: Is this what you are looking for? This is based on what I gathered from your request, but it is absolutely possible that I misunderstand your data structure. - Thorsten Kettner

It's perfect, and definitely does what I asked for (just finished checking it). Too bad MySQL can't show me a list of the ignored rows, which means that I need to select all bets with userId, compare, and then return the user/client which bet was placed and which wasn't..Well thx a lot, works like a charm:) - chico_m

And just in case I'll decide to use it instead, do you have any idea of how to cancel the WHOLE query if at least one of these selects results in EXISTS (meaning the game started/finished) - chico_m

I've edited my answer to give you a solution for this. - Thorsten Kettner

have you tried with UNION ?

 INSERT INTO bet_on_event (user_id, event_id, bet)
 (SELECT 1,5,1 FROM dual
  WHERE (SELECT COUNT(*) FROM events WHERE _id IN(5,6) AND status=0) = ?
 UNION 
 SELECT 1,6,2 FROM dual
 WHERE (SELECT COUNT(*) FROM events WHERE _id IN(5,6) AND status=0) = ? );

contestado el 28 de mayo de 14 a las 13:05

Two queries in parentheses and a where clause outside both? I suppose this is syntactically incorrect. BTW: There is no need for UNION here, as 1,5,1 will never be the same as 1,6,1. No duplicates to remove hence, so better use UNION ALL. - Thorsten Kettner

Now that you changed the parentheses, the query after UNION has a where clause and the query before UNION does not. - Thorsten Kettner

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