在PL/SQL中添加约束

Question

我有两张桌子:

Employee(eid, ename, age..)
Department(deptid, dname, managerid..) //manager id references eid

如何在Department表上创建约束,使经理的年龄始终> 25？

Answer 1

约束不能包含子查询,因此如果要在数据库级别强制执行此业务规则,则需要触发器.像这样的东西.

create or replace trigger dep_briu_trg
  before insert or update on department  
  for each row
declare
  l_age employee.age%type;   

    begin
       select age
       into l_age
       from empoyee
       where id=:new.managerid;

       if l_age<=25 then
        raise application_error(-20000,'Manager is to young');
       end if;
    exception
       when no_data_found then
        raise application_error(-20000,'Manager not found');
    end;

BTW永远不要把年龄存放在桌子上.它每天都不同.

Answer 2

在Oracle 11g中,您可以使用虚拟列作为外键的目标:

CREATE TABLE emp (eid NUMBER PRIMARY KEY,
                  age NUMBER NOT NULL,
                  eligible_mgr_eid AS (CASE WHEN age > 25 THEN eid ELSE NULL END) UNIQUE
                 );

CREATE TABLE dept (did NUMBER PRIMARY KEY,
                   mgr_id NUMBER NOT NULL REFERENCES emp (eligible_mgr_eid) );