self referencing table

Question

I have a table like this,

  table name = staff
  staff-id(pk), last-name, first-name, job-title, reports-to(fk)

Reports to is a self referencing key.

I already have data to insert in to this table. In my data all the staff members have reports-to person but MD does not have a reports-to person as MD is the highest position. So as it references to no key how can I create table as a self referencing foreign key because insertion will probably cause a problem.

Data to MD column is

staff-id last-name first-name job-title reports-to

200 Vellum Harry MD 0

   CREATE TABLE staff
    ( staff-id number not null,
     last-name varchar2(20) not null,
     first-name varchar2(20),
     job-title varchar2(20) not null,
     reports-to number not null,
     CONSTRAINT staffid_pk PRIMARY KEY (staff-id)
     CONSTRAINT reportsto_fk FOREIGN KEY (staff-id) REFERENCES staff(staff-id)
     );

Can I have MD's reports-to key as his primary key, if so again adding will cause a problem. How to solve this problem? I'm using oracle 11g

Answer 1

要么将MD报告设置为self（即，将Reports-To列设置为staff-id列值），要么将Reports-To列设置为可空（外键列可以等于NULL ）