我将如何创建一个触发器来检查一个值以确保它是正确的值，否则将引发错误？

Question

 DROP TABLE Officer cascade constraints;
 CREATE TABLE Officer(
 StaffID        Number(6)  PRIMARY KEY,
 FirstName    VARCHAR2(16),
 MiddleName    VARCHAR2(16),
 Surname    VARCHAR2(16),
 Rank    VARCHAR2(16),
 Department    VARCHAR2(16),
 Place_Of_Work   VARCHAR2(16),
 Hire_Date   VARCHAR2(16),
 Inspector_ID    Number(6));

 alter table Officer
  add constraint Officer_Inspector_ID_FK
  foreign key ( Inspector_ID )
  references Officer ( StaffID )
  on delete set null
  ;

 create sequence Officer_seq start with 100 increment by 1 nomaxvalue; 
 create trigger Officer_trigger
 before insert on Officer
 for each row
 begin
 select Officer_seq.nextval into :new.StaffID from dual;
   end;​

What I want to do is make it so that if an inspector ID is entered for an officer that doesn't match up to an officer that has the rank of inspector then it will throw an error that states they aren't an inspector & will prompt them to enter a valid ID.

Answer 1

no trigger required

What you are describing is a multi-foreign key constraint from Officer(Inspector_id, Inspector_rank) to Officer(Staff_id, rank)

you need to add the inspector_rank field to officer table

then you need to link both id and rank to officer together so they are both the same record

foreign key (Inspector_id, Inspector_rank) references Officer(Staff_id, rank)

then you need a simple value constraint of inspector_rank CHECK inspector_rank = INSEPECTOR