数据库中不同实体的相同数据 - 最佳实践 - 电话号码示例

Question

鉴于一个数据库系统处理员工,客户和供应商,所有这些都有多个可能的电话号码,您将如何以良好的标准化方式存储这些数字？我有一点思考,合乎逻辑的方式并没有跳出来.

Answer 1

在多数情况下 ...

• "员工"总是描述人.
• 有些客户是人.
• 一些客户是企业(组织).
• "供应商"通常是(总是？)组织.
• 员工也可以是客户.
• 供应商也可以是客户.

使用单独的员工电话号码,供应商电话号码和客户电话号码表存在严重问题.

• 员工可以是客户.如果员工电话号码发生变化,客户电话号码是否也需要更新？你怎么知道更新哪一个？
• 供应商可以是客户.如果供应商的电话号码发生变化,是否还需要更新客户电话号码？你怎么知道更新哪一个？
• 您必须在存储电话号码的每个表中复制并维护没有错误的电话号码限制.
• 当客户的电话号码发生变化时,会出现同样的问题.现在您必须检查员工和供应商电话号码是否也需要更新.
• 要回答"谁的电话号码是123-456-7890？"这个问题,你必须查看'n'个不同的表格,其中'n'是你处理的不同"种类"的派对.除了员工,客户和供应商之外,还要考虑"承包商的电话","潜在客户的电话"等.

您需要实现超类型/子类型架构.(PostgreSQL代码,未经过严格测试.)

create table parties (
    party_id integer not null unique,
    party_type char(1) check (party_type in ('I', 'O')),
    party_name varchar(10) not null unique,
    primary key (party_id, party_type)
);

insert into parties values (1,'I', 'Mike');
insert into parties values (2,'I', 'Sherry');
insert into parties values (3,'O', 'Vandelay');

-- For "persons", a subtype of "parties"
create table person_st (
    party_id integer not null unique,
    party_type char(1) not null default 'I' check (party_type = 'I'),
    height_inches integer not null check (height_inches between 24 and 108),
    primary key (party_id),
    foreign key (party_id, party_type) references parties (party_id, party_type) on delete cascade
);

insert into person_st values (1, 'I', 72);
insert into person_st values (2, 'I', 60);

-- For "organizations", a subtype of "parties"
create table organization_st (
    party_id integer not null unique,
    party_type CHAR(1) not null default 'O' check (party_type = 'O'),
    ein CHAR(10), -- In US, federal Employer Identification Number
    primary key (party_id),
    foreign key (party_id, party_type) references parties (party_id, party_type) on delete cascade
);

insert into organization_st values (3, 'O', '00-0000000');

create table phones (
    party_id integer references parties (party_id) on delete cascade,
    -- Whatever you prefer to distinguish one kind of phone usage from another.
    -- I'll just use a simple 'phone_type' here, for work, home, emergency, 
    -- business, and mobile.
    phone_type char(1) not null default 'w' check 
        (phone_type in ('w', 'h', 'e', 'b', 'm')),
    -- Phone numbers in the USA are 10 chars. YMMV.
    phone_number char(10) not null check (phone_number ~ '[0-9]{10}'),
    primary key (party_id, phone_type)
);

insert into phones values (1, 'h', '0000000000');
insert into phones values (1, 'm', '0000000001');
insert into phones values (3, 'h', '0000000002');

-- Do what you need to do on your platform--triggers, rules, whatever--to make 
-- these views updatable. Client code uses the views, not the base tables.
-- In current versions of PostgreSQL, I think you'd create some "instead
-- of" rules.
--
create view people as
select t1.party_id, t1.party_name, t2.height_inches
from parties t1
inner join person_st t2 on (t1.party_id = t2.party_id);

create view organizations as 
select t1.party_id, t1.party_name, t2.ein
from parties t1
inner join organization_st t2 on (t1.party_id = t2.party_id);

create view phone_book as
select t1.party_id, t1.party_name, t2.phone_type, t2.phone_number
from parties t1
inner join phones t2 on (t1.party_id = t2.party_id);

为了进一步扩展这一点,实现"工作人员"的表需要引用人员子类型,而不是派对超类型.组织不能是员工.

create table staff (
    party_id integer primary key references person_st (party_id) on delete cascade,
    employee_number char(10) not null unique,
    first_hire_date date not null default CURRENT_DATE
);

如果供应商只能是组织而不是个人,那么实施供应商的表格将以类似的方式引用组织子类型.

对于大多数公司而言,客户可以是个人或组织,因此实现客户的表应该引用超类型.

create table customers (
    party_id integer primary key references parties (party_id) on delete cascade
    -- Other attributes of customers
);