第一眼看到mysql的trigger，感觉和其他数据库的trigger是一样的，或者说所有的SQL语法都是类似的.
注意：如果要更新NEW的数据，必须使用before
syntax AS
delimiter |
create trigger test_trig [before,after] [insert,update,delete] on test
for each row
begin
insert into test2 values( "nice to use trigger" );
update test set cm1=( select name from test3 where id=NEW.t3id );
//NEW
//OLD
/*...
