mysql触发器

向mysql写入触发器时

create trigger test

before update on tablename  for each row 

begin

  update tablename set NEW.col = ' ';

end

写入正常，但在更新数据时一直出现：

ERROR 1442 (HY000): Can't update table 'tablename' in stored function/trigger becau

se it is already used by statement which invoked this stored function/trigger

原因是触发器在更新本表时触发了触发器，会导致循环调用。

因此需要在触发器中使用set，而不是update。

before update on tablename  for each row 

begin

  set NEW.col = ' ';

end

直接如上就完事了。

附上最近做项目时的一个完整的触发器结构，以备以后使用：

use hotel;

DROP TRIGGER IF EXISTS `triggerForLevelChange`; 

create trigger triggerForLevelChange

BEFORE update on vip

for each row

begin

if new.padmoney>='200' and new.padmoney<='300' then   

set NEW.lid='2' ;

ELSEif new.padmoney>='300' and new.padmoney<='400' then   

set NEW.lid='3' ;

ELSEif new.padmoney>='400' and new.padmoney<='500' then   

set NEW.lid='4' ;

ELSEif new.padmoney>='500' and new.padmoney<='600' then   

set NEW.lid='5' ;

ELSEif new.padmoney>='600' then   

set NEW.lid='6' ;

end if;

end;