SQL创建表依赖关系 [英] SQL Creating Table Dependencies

问题描述

我一直坚持创建表。

这里是我坚持如何使代码在 loan_type <中工作的代码/ code>写办公室工作人员或非办公室工作人员

Here is the code I am stuck at how to make the code work in loan_type to write office worker or non office worker

create table loaner 
(
   loan_id number(5) primary key,
   loan_type VARCHAR2 (16),
   loan_start_date date,
   loan_end_date date,
)

create table office_worker 
(
   worker_id number(5) primary_key,
   loan_id number(5) references loaner(loan_id),
   worker_name varchar2(50)
)

create table nonoffice_worker 
(
   nonworker_id number(5) primary_key,
   loan_id number(5) references loaner(loan_id),
   nonworker_name varchar2(50)
);

commit;

推荐答案

您无法创建约束来检查现有的表格结构。常见的做法是这样的：

You can't create a constrain to check that with the existing table structures. A common way to do it is like this:

create table loaner (
loan_id number(5) primary key,
loan_type VARCHAR2 (16),
loan_start_date date,
loan_end_date date,
constraint loaner_uk unique (loan_id, loan_type)
);

create table office_worker (
worker_id number(5) primary_key,
loan_id number(5),
loan_type VARCHAR2 (16),
worker_name varchar2(50),
constraint office_worker_loaner_fk foreeign key (loan_id, loan_type) references loaner (loan_id, loan_type),
constraint office_worker_loan_type_chk check (loan_type = 'OFFICE')
);

create table nonoffice_worker (
nonworker_id number(5) primary_key,
loan_id number(5),
loan_type VARCHAR2 (16),
nonworker_name varchar2(50),
constraint nonoffice_worker_loaner_fk foreeign key (loan_id, loan_type) references loaner (loan_id, loan_type),
constraint nonoffice_worker_loan_type_chk check (loan_type = 'NONOFFICE')
);

即：

1. 在第一个表的（load_id，loan_type）中创建一个冗余的UNIQUE约束。


2. 在子类型表中添加loan_type并将外键基于（loan_id，loan_type）。


3. 向每个子类型表添加检查约束，以确保使用正确的loan_type。

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