MySQL错误-无法更新存储的函数/触发器中的表'library_audit2'，因为该语句已使用该表

问题描述

在删除记录时，它给了我一个错误。触发器中的问题出在哪里。

MysqL代码-

MariaDB [practice2]> delimiter $$
MariaDB [practice2]> create trigger BeforeLibraryDelete1
    -> BEFORE DELETE
    -> ON library_audit2 FOR EACH ROW
    -> BEGIN
    -> declare id1 int;
    -> select library_id into id1 from library_audit2 where change_date=OLD.change_date;
    -> delete from library_2 where library_2.id=id1;
    -> END $$
Query OK,0 rows affected (0.128 sec)

MariaDB [practice2]> delimiter ;


MariaDB [practice2]> Delete from library_audit2 where change_date='2017-04-07';

在触发删除查询时，出现错误-

ERROR 1442 (HY000): Can't update table 'library_audit2' in stored function/trigger because it is already used by statement which invoked this stored function/trigger

解决方法

您有一个针对每行触发的删除触发器。我真的没有看到再次从源表中进行选择只是为了获取要删除的行的ID的意义。该信息已在触发器级别的伪列old.id1中提供。

这不是您想要的吗？

create trigger beforelibrarydelete1
before delete on library_audit2 
for each row
begin
    delete from library_2 where id = old.id;
end $$

阅读问题下的注释，似乎您正在尝试使用此触发器处理外键依赖性。如果您在library2中有引用library_audit2的子记录，那么只要从父表中删除记录，就可以使用on delete cascade选项自动删除它们。

create table library2 (
    ...
    foreign key (id)
        references library_audit2(id)
        on delete cascade
);