mysql trigger使用笔记
trigger语法：
CREATE TRIGGER trigger_name trigger_time trigger_event
    ON tbl_name FOR EACH ROW trigger_stmt
例如：
DELIMITER $$
USE `gjp`$$
CREATE
DEFINER=`root`@`localhost`
TRIGGER `gjp`.`end_it`
BEFORE UPDATE ON `gjp`.`gjp$abc`
FOR EACH ROW
BEGIN
if NEW.time=0 then
    set NEW.end_time=current_timestamp;
end if;
END$$
需要注意的是如果trigger由一个update触发而执行的update语句，需要用set，而不能直接用update语句，如上面那个trigger的if NEW.time=0 then set NEW.end_time=current_timestamp不能写成update gjp$abc set gjp$abc.end_time = current_timestamp where gjp$abc.time=0;否则会形成循环而报Can't update table 'gjp$abc' in stored function/trigger because it is already used by statement which invoked this stored function/trigger.
还需注意这里的trigger_time需是before.