[英]Adding constraint in PL/SQL
I have two tables: 我有两个表:
Employee(eid, ename, age..)
Department(deptid, dname, managerid..) //manager id references eid
How can I create a constraint on Department table such that manager's age is always > 25 ? 如何在Department表上创建约束,以使经理的年龄始终> 25?
A constraint cannot contain a subquery so a trigger is needed if you want to enforce this business rule on database level. 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。 Something like this. 这样的事情。
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 Never store age in a table. 顺便说一句永远不要将年龄存储在表中。 It's different every day. 每天都不同。
In Oracle 11g, you could use a virtual column to be the target of a foreign key: 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) );
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