如何避免MySQL中的循环触发器依赖

我在MySQL中使用触发器有一点问题.

假设我们有2个表：

>表A
>表B.

和2个触发器：

> TriggerA：在TableA上删除时触发并更新TableB
> TriggerB：在TableB上删除时触发并在TableA中删除

问题是当我删除TableB中的某些行时,TriggerB会触发并删除TableA中的某些元素,然后触发TriggerA并尝试更新TableB.

它失败,因为TriggerA尝试更新TableB中正在删除的某些行.

我怎样才能避免这种循环依赖？

这两个触发器都没用,所以我不知道我该怎么做才能解决这个问题.

解决方法:

尝试使用变量.

第一次触发：

CREATE TRIGGER trigger1
  BEFORE DELETE
  ON table1
  FOR EACH ROW
BEGIN
  IF @deleting IS NULL THEN
    SET @deleting = 1;
    DELETE FROM table2 WHERE id = OLD.id;
    SET @deleting = NULL;
  END IF;
END

第二次触发：

CREATE TRIGGER trigger2
  BEFORE DELETE
  ON table2
  FOR EACH ROW
BEGIN
  IF @deleting IS NULL THEN
    SET @deleting = 1;
    DELETE FROM table1 WHERE id = OLD.id;
    SET @deleting = NULL;
  END IF;
END

额外的AFTER DELETE触发器：

CREATE TRIGGER trigger3
  AFTER DELETE
  ON table1
  FOR EACH ROW
BEGIN
  SET @deleting = NULL;
END

CREATE TRIGGER trigger4
  AFTER DELETE
  ON table2
  FOR EACH ROW
BEGIN
  SET @deleting = NULL;
END

标签：mysql,triggers,circular-dependency
来源： https://codeday.me/bug/20190609/1208201.html