mysql TRIGGER update field after update - mysql

Question

i have 2 table today_plan and kiln_master.
after pattern and itemno inserted to today_plan then need to select matching yeild from kiln_master table and update this value to yeild field in today_plan.
i have created a trigger
CREATE TRIGGER update_yeild AFTER INSERT ON today_plan
FOR EACH ROW UPDATE today_plan
SET yeild= (SELECT kiln_master.yeild from kiln_master,today_plan WHERE today_plan.itemno = kiln_master.item AND today_plan.pattern = kiln_master.pattern ) WHERE itemno=new.itemno AND pattern=new.pattern
what part is wrong with my code
today_plan
DROP TABLE IF EXISTS decsys.today_plan;
CREATE TABLE `today_plan` (
`id` int(10) unsigned NOT NULL AUTO_INCREMENT,
`belt` varchar(25) NOT NULL,
`distant` varchar(25) NOT NULL,
`pjtno` varchar(15) DEFAULT NULL,
`pattern` varchar(25) NOT NULL,
`itemno` varchar(25) NOT NULL,
`pro_qty` varchar(25) NOT NULL,
`act_qty` varchar(25) NOT NULL,
`yeild` varchar(25) NOT NULL,
`remark` varchar(100) NOT NULL,
`shipment` varchar(15) NOT NULL,
`temp` varchar(15) NOT NULL,
`fire_date` date NOT NULL,
`kiln` varchar(10) DEFAULT NULL,
`kiln_plan` varchar(15) NOT NULL,
`kiln_act` varchar(15) NOT NULL,
`ins_date` date NOT NULL,
`ins_act` varchar(15) NOT NULL,
`plandate` date NOT NULL,
`ship_date` date NOT NULL,
PRIMARY KEY (`id`)
) ENGINE=MyISAM AUTO_INCREMENT=31 DEFAULT CHARSET=utf8;
kiln_master
DROP TABLE IF EXISTS decsys.kiln_master;
CREATE TABLE `kiln_master` (
`kid` int(7) NOT NULL,
`pattern` varchar(30) NOT NULL,
`item` varchar(30) NOT NULL,
`yeild` double NOT NULL,
`temp` int(6) NOT NULL,
`kiln` varchar(10) NOT NULL
) ENGINE=InnoDB DEFAULT CHARSET=latin1;
error
#1442 - Can't update table 'today_plan' in stored function/trigger because it is already used by statement which invoked this stored function/trigger.
thank you very much

Answer 1

You're trying to update the row after it has been inserted, isn't it better to do before so that it gets inserted with the correct values? That'd be something like;
CREATE TRIGGER update_yeild BEFORE INSERT ON today_plan
FOR EACH ROW
SET NEW.yeild = COALESCE((SELECT kiln_master.yeild
FROM kiln_master
WHERE NEW.itemno = kiln_master.item
AND NEW.pattern = kiln_master.pattern
LIMIT 1), 0);