如何使触发器像外键一样工作？

Question

我需要使用触发器创建一个外键，而不是像这样只使用一个改变 table：

 alter table WORKER
      add constraint WORKER_idDepartment_FK
      foreign key (idDepartment)
      references DEPARTMENT (idDepartment);

有人可以帮我吗？

Answer 1

在极少数情况下，您会放弃标准的 FOREIGN KEY 机制以支持其他机制。例如，我们有一个非常庞大的 table 数据库，其中创建了数十个 FK。这些外键占用了数百兆的磁盘 space。就其性质而言，他们引用 table 的记录数比主 table 少 10000-100000 倍。切换到触发器以支持数据完整性后，我们显着减少了数据库文件的大小，并获得了一些整体性能提升。

像这样的外键：

 alter table WORKER
      add constraint WORKER_idDepartment_FK
      foreign key (idDepartment)
      references DEPARTMENT (idDepartment);

可以用两个触发器模拟：

 CREATE TRIGGER aiu_worker FOR WORKER
   AFTER INSERT OR UPDATE
   POSITION 0
 AS BEGIN
   IF (NOT EXISTS(
      SELECT idDepartment 
      FROM DEPARTMENT 
      WHERE idDepartment = NEW.idDepartment)) THEN
    EXCEPTION my_exception 'There is no department with id=' ||
      NEW.idDepartment;
 END

 CREATE TRIGGER ad_department FOR DEPARTMENT
   AFTER DELETE
   POSITION 0
 AS BEGIN
   IF (EXISTS (
       SELECT idDepartment 
       FROM WORKER 
       WHERE idDepartment = OLD.idDepartment)) THEN
   BEGIN
     EXCEPTION my_exception 'Can not delete record';
   END
 END

您可以轻松调整这些触发器以实施 CASCADE 规则或支持可为空的字段。

如何使触发器像外键一样工作？

How to make a Trigger work like a Foreign Key?

sql

database

firebird