Simple Oracle Database schema.

company.sql

-- The database schema used in the second half of the following tutorial:
--
-- https://www.youtube.com/watch?v=HXV3zeQKqGY
--
-- Adapted to Oracle Database.

create table employee (
  id int not null,
  first_name varchar(20) not null,
  last_name varchar(20) not null,
  birth_date date not null,
  -- A cool thing to learn is if I can require this to be 'f' or 'm'.
  sex varchar(1) not null,
  salary int not null,
  -- Only supervisor and branch can be `NULL`.
  supervisor int,
  branch int
);

alter table employee add constraint employee_pk primary key (id);
-- `on delete` specifies what to do if the referenced employee is deleted.
-- Without this, referenced employees won't be deleteable.
alter table employee add constraint employee_supervisor_fk foreign key (supervisor) references employee (id) on delete set null;

create table branch (
  id int not null,
  branch_name varchar(20) not null,
  manager int not null,
  manager_start_date date not null
);

alter table branch add constraint branch_pk primary key (id);
alter table branch add constraint branch_manager_fk foreign key (manager) references employee (id) on delete set null;

alter table employee add constraint employee_branch_fk foreign key (branch) references branch (id) on delete set null;

create table client (
  id int not null,
  name varchar(20) not null,
  branch int not null
);

alter table client add constraint client_pk primary key (id);
alter table client add constraint client_branch_fk foreign key (branch) references branch (id) on delete set null;

create table works_with (
  employee int not null,
  client int not null,
  total_sales int default 0 not null
);

alter table works_with add constraint works_with_pk primary key (employee, client);
-- If the referenced employee or client is deleted so will the corresponding
-- entries in this table.
alter table works_with add constraint works_with_employee_fk foreign key (employee) references employee (id) on delete cascade;
alter table works_with add constraint works_with_client_fk foreign key (client) references client (id) on delete cascade;

create table branch_supplier (
  branch int not null,
  name varchar(20) not null,
  type varchar(20) not null
);

alter table branch_supplier add constraint branch_supplier_pk primary key (branch, name);
alter table branch_supplier add constraint branch_supplier_branch_fk foreign key (branch) references branch (id) on delete cascade;