create table customer (
	customer_id	int not null,
	customer_type char( 1 ) not null, check (customer_type in ('P','O')),
	-- Общие атрибуты клиентов
	-- ...
	constraint PK primary key (customer_id,customer_type)
)@


create table people (
	customer_id	int not null,
	customer_type char( 1 ) not null check (customer_type in ('P')),
	-- Дополнительные атрибуты физ лиц
	-- ...
	constraint FK foreign key (customer_id,customer_type)
		references customer (customer_id,customer_type)
			on delete restrict on update restrict,
	constraint PK primary key (customer_id,customer_type)
)@


create table organization (
	customer_id	int not null,
	customer_type char( 1 ) not null check (customer_type in ('O')),
	-- Дополнительные атрибуты юр лиц
	-- ...
	constraint FK foreign key (customer_id,customer_type)
		references customer (customer_id,customer_type)
			on delete restrict on update restrict,
	constraint PK primary key (customer_id,customer_type)
)@

-- Как пример:
create table Doc (
	-- Производитель
	org_id int,
	org_type char( 1 ),
	-- Потребитель
	fl_id int,
	fl_type char( 1 ),
	-- Прочие атрибуты
	-- ...
	constraint FK_PEOPLE foreign key (org_id,org_type) references people (customer_id, customer_type),
	constraint FK_ORG foreign key (fl_id,fl_type) references organization (customer_id, customer_type)
)@

create table customer (
	customer_id	int not null,
	customer_type char( 1 ) not null, check (customer_type in ('P','O')),
	-- Общие атрибуты клиентов
	-- ...
              
               constraint PK primary key (customer_id),
               constraint PK2 unique (customer_id,customer_type)
)@

create table people (
	customer_id	int not null,
	customer_type char( 1 ) not null check (customer_type in ('P')),
	-- Дополнительные атрибуты физ. лиц
	-- ...
	constraint FK foreign key (customer_id,customer_type)
		references customer (customer_id,customer_type)
			on delete restrict on update restrict,
	constraint PK primary key (customer_id)
)@



create table organization (
	customer_id	int not null,
	customer_type char( 1 ) not null check (customer_type in ('O')),
	-- Дополнительные атрибуты юр. лиц
	-- ...
	constraint FK foreign key (customer_id,customer_type)
		references customer (customer_id,customer_type)
			on delete restrict on update restrict,
	constraint PK primary key (customer_id)
)@