表格设计问题，用于规范共享相似数据的多个类别

Question

I'm little confused in a table design.

Method 1) With first method i can select all phone number from phone_book table and filter out employee phone numbers by specifying type. Method 2) In second method i can select all by joining two table and can retrieve employee phone numbers.

I've same issue with addresses. I've address of employees, customers, staffs and others. I've googled and still cant choose which is right method. Which is the right method and why the other not and any other better design for this ?

employee
id | name 
1      e


customer
id | name
1     c


phone_book
type | fk_id |     phone
  e      1         123123123
  c      1         451323123

employee
id | name 
1      e


customer
id | name
1     c


employee_phone_book
emp_id  |     phone
   1         1231233434
   2         6273343423


customer_phone_book
cus_id  |  phone
   1       5231233434
   2       1251233434

Edit: Employee and customers can have multiple phone numbers. And same with the address details.

Answer 1

employee
id | name | phone_id
1      e    1


customer
id | name | phone_id
1     c     2


phone_book
phone_id |     phone
1         123123123
2         451323123

For me the reference to phone should be in the employee and customer tables (FK to the phone_book table)

UPDATE: If customer/employee may have multiple phones it would be better to define many-to-many relations via additional table eg

customer_phone 
phone_id |     customer_id (reference to the customer table)
1              1
2              1

Answer 2

If employee and customers are having multiple phone numbers than your phone_book should look something like this. you need to create one is to many relation table structure.

phone_book
phone_id | EmpOrCustomer | EmpOrCustomerId | phone
1          1               1                  123123123
2          1               1                  45132XXXX
3          2               4                  45132XXXX

In the above table structure, you can add two additional column which tells you its employee or customer, another which tells what is the employee or customer id.

Hope this helps.