Calculate value based on sub squery in Trigger - mysql

Question

I want to create a trigger in MySql to insert some values in table A and if the record already exist I want to re-calculate one of the fields but I'm keep getting a syntax error:
1064 - You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near 'P1
INNER JOIN
(
SELECT SUM(ATS) AS TOTAGAINST, TOURNID, HOMETEAM, ROUNDID' at line 6
Here's my code (stripped for debugging):
DROP TRIGGER IF EXISTS `trig_matches_insert`;
DELIMITER //
CREATE TRIGGER `trig_matches_insert` AFTER INSERT ON `matches`
FOR EACH ROW
BEGIN
INSERT INTO positions (TEAMID, SC_AGAINST, SC_FOR, ROUNDID, TOURNID) values
(new.HOMETEAM, new.ATS, new.HTS, new.ROUNDID, new.TOURNID)
ON DUPLICATE KEY
UPDATE positions P1
INNER JOIN
(
SELECT SUM(ATS) AS TOTAGAINST, TOURNID, HOMETEAM, ROUNDID FROM matches GROUP BY
TOURNID,HOMETEAM, ROUNDID
) P2 ON P2.HOMETEAM = P1.TEAMID AND P2.TOURNID = P1.TOURNID AND P2.ROUNDID = P1.ROUNDID
SET P1.SC_AGAINST = P2.TOTAGAINST WHERE P1.ID = 10;
END
//
DELIMITER ;
I can't tell what's wrong here..
When I run the update query stand-alone it runs fine
Here's some supporting sql:
CREATE TABLE IF NOT EXISTS `matches` (
`ID` int(11) NOT NULL AUTO_INCREMENT,
`TOURNID` int(11) NOT NULL,
`HOMETEAM` int(11) NOT NULL,
`AWAYTEAM` int(11) NOT NULL,
`HTS` decimal(10,0) NOT NULL,
`ATS` decimal(10,0) NOT NULL,
`FIELD` text NOT NULL,
`TIME` datetime NOT NULL,
`ROUNDID` int(11) NOT NULL,
PRIMARY KEY (`ID`),
KEY `TOURNID` (`TOURNID`),
KEY `HOMETEAM` (`HOMETEAM`),
KEY `AWAYTEAM` (`AWAYTEAM`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8 AUTO_INCREMENT=20 ;
INSERT INTO `matches` (`ID`, `TOURNID`, `HOMETEAM`, `AWAYTEAM`, `HTS`, `ATS`, `FIELD`, `TIME`, `ROUNDID`) VALUES
(17, 1, 30, 31, '2', '3', '', '2015-01-04 00:00:00', 1),
(18, 1, 30, 3, '2', '4', '', '2015-01-04 00:00:00', 1),
(19, 1, 30, 4, '3', '5', '', '2015-01-04 00:00:00', 1);
CREATE TABLE IF NOT EXISTS `positions` (
`ID` int(11) NOT NULL AUTO_INCREMENT,
`TOURNID` int(11) NOT NULL,
`TEAMID` int(11) NOT NULL,
`ROUNDID` int(11) NOT NULL,
`SC_FOR` decimal(10,0) NOT NULL,
`SC_AGAINST` decimal(10,0) NOT NULL,
`POULEID` int(11) NOT NULL,
PRIMARY KEY (`ID`),
UNIQUE KEY `TOURNID_2` (`TOURNID`,`TEAMID`,`ROUNDID`),
KEY `TOURNID` (`TOURNID`,`TEAMID`),
KEY `TEAMID` (`TEAMID`),
KEY `ROUND` (`ROUNDID`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8 AUTO_INCREMENT=15 ;
INSERT INTO `positions` (`ID`, `TOURNID`, `TEAMID`, `ROUNDID`, `SC_FOR`, `SC_AGAINST`, `POULEID`) VALUES
(10, 1, 30, 1, '2', '12', 0);
Thanks in advance
Mike

Answer 1

Think I've found it, looks like after ON DUPLICATE KEY the positions table already got scope no need to build and update statement from scratch, seems like a quick select will do just fine:
DROP TRIGGER IF EXISTS `matches_after_ins_trig`;
DELIMITER //
CREATE TRIGGER `matches_after_ins_trig` AFTER INSERT ON `matches`
FOR EACH ROW
BEGIN
INSERT INTO positions (TEAMID, SC_AGAINST, SC_FOR, ROUNDID, TOURNID) values (new.HOMETEAM, new.ATS, new.HTS, new.ROUNDID, new.TOURNID)
ON DUPLICATE KEY UPDATE SC_AGAINST = (SELECT SUM(ATS) FROM matches WHERE
matches.HOMETEAM = new.HOMETEAM AND matches.TOURNID = new.TOURNID AND
matches.ROUNDID = new.ROUNDID GROUP BY TOURNID,HOMETEAM, ROUNDID);
END