MySQL程序返回错误的值（INSERT SELECT面对）

Question

I'm completely new to MySQL, and have been bumping with some errors, but always I do find solutions, except for this one I can't understand how to get around it.

The following MySQL Procedure returns me a value if variable "ue" is 1 or 0 (a bunch of exists validation). The validation part (SET ue = EXISTS...) works without the rest of the code, as it should, the problem is not there. But when I do execute the command INSERT INTO SELECT, it does not work, it always return 0 as response, when it should be 1. These two lines are getting in confrontation with each other.

INSERT INTO meetup_participation SELECT user_id, event_id FROM DUAL WHERE ue=1;

SELECT ue AS response;

The procedure should add 'user id' and 'event id' into meetup_participation, and then update the row at 'users' corresponding to the user with that 'user id' to increment the 'events participated'. And it also UPDATE to increment the participation in the event with this 'event id'.

I am using the SET ue to validate things like, if user exists, if event does exists, if date of event is still valid, and if user is not already in this table. So I am passing this value as a boolean to INSERT INTO meetup_participation [...] WHERE ue = 1. After that, I do SELECT ue to inform validation returned true and procedure executed without problems.

Here is the full procedure.

CREATE DEFINER=`user`@`localhost` PROCEDURE `join_event`(IN `user_id` BIGINT(64), IN `event_id` INT) NOT DETERMINISTIC MODIFIES SQL DATA SQL SECURITY DEFINER

begin 

DECLARE ue INT;
SET ue = EXISTS(SELECT 1 FROM users WHERE fb_uid=user_id) AND EXISTS(SELECT 1 FROM meetup WHERE meet_id=event_id) AND EXISTS(SELECT 1 FROM meetup WHERE date > NOW() AND meet_id = event_id) AND EXISTS(SELECT 1 FROM meetup WHERE meet_id = event_id AND participants <= max_participants) AND NOT EXISTS(SELECT 1 FROM meetup_participation WHERE fb_uid = user_id AND meet_id = event_id);

INSERT INTO meetup_participation SELECT user_id, event_id FROM DUAL WHERE ue=1; 

UPDATE users SET events_participated = events_participated + 1 WHERE fb_uid=user_id AND ue=1; 
UPDATE meetup SET participants = participants + 1 WHERE meet_id=event_id AND ue=1; 
SELECT ue AS response; 

end

Thanks in advance.

Answer 1

The INSERT statement is executed separately from the SET ue =... statement. I'm not sure what you are trying to accomplish, but the code makes no sense.

If you want to add records to meetup_participation based on the EXISTS tests applied to each record in the users table, you would need to apply the tests to each record in your SELECT statement as part of the INSERT.

There are also numerous syntax/grammar issues in the code as shown.

If you could provide an explanation of what you are trying to accomplish with the procedure, that might allow someone to suggest the right way to code the procedure.

Answer 2

Selecting ue will not tell you if the procedure completed without error. You should research mysql transactions and mysql error handling. http://www.mysqltutorial.org/mysql-error-handling-in-stored-procedures/ is a good starting point.

You might end up with something like this

drop procedure if exists p;
delimiter //

CREATE DEFINER=`root`@`localhost` PROCEDURE `p`(
    IN `inue` int,
    IN `user_id` BIGINT(64),
    IN `event_id` INT
)
LANGUAGE SQL
NOT DETERMINISTIC
MODIFIES SQL DATA
SQL SECURITY DEFINER
COMMENT ''
begin 

DECLARE ue INT;
declare exit handler for sqlexception
begin
    rollback;
    insert into errors (msg) select concat('error ' ,inue,',',user_id,',',event_id);
end;

set autocommit = 0;
#set ue = inue;
 SET ue = EXISTS(SELECT 1 FROM users WHERE fb_uid=user_id) 
    AND EXISTS(SELECT 1 FROM meetup WHERE meet_id=event_id) 
    #AND EXISTS(SELECT 1 FROM meetup WHERE dt > NOW() AND meet_id = event_id) 
    AND EXISTS(SELECT 1 FROM meetup WHERE meet_id = event_id AND ifnull(participants,0) <= max_participants) 
    AND NOT EXISTS(SELECT 1 FROM meetup_participation WHERE fb_uid = user_id AND meet_id = event_id)
    ;
select ue;

if ue = 1 then

start transaction;

INSERT INTO meetup_participation SELECT user_id, event_id,user_id, event_id; 
UPDATE users SET events_participated = ifnull(events_participated,0) + 1 WHERE fb_uid=user_id = user_id; 
UPDATE meetup SET participants = ifnull(participants,0) + 1 WHERE meet_id = event_id ; 

commit;

end if;

SELECT ue AS response; 

end //

The error table looks like this

CREATE TABLE `errors` (
  `msg` varchar(2000) DEFAULT NULL,
  `id` int(11) NOT NULL AUTO_INCREMENT,
  PRIMARY KEY (`id`)
) ENGINE=InnoDB AUTO_INCREMENT=2 DEFAULT CHARSET=latin1

Note I am not suggesting this is a solution appropriate to your site , you need to do the research and figure out what is best for you.