Create table aluno (
Id integer not null,
Nom_aluno char(30) not null,
Cod_hobby smallint,
Primary key (id)
);

Create table hobby (
Cod_hobby smallint not null,
Des_hobby char(30) not null,
Primary key (cod_hobby)
);

Alter table aluno add constraint fk_hobby foreign key (cod_ hobby)

References hobby (cod_hobby) on delete set null

On update set null;

Insert into hobby (cod_hobby, des_hobby) values
(1, ‘Jogar vídeo game’),
(2, ‘Jogar futebol’),
(3, ‘Andar de Bike’);

Insert into aluno (id, nom_aluno, cod_hobby) values
(1, ‘Antônio Vieira Santos’, NULL),
(2, ‘Joana Pereira’, 3),
(3, ‘Maurício Antunes’, 1),
(4, ‘Paulo da Silva’, NULL);

Observe os comandos SQL, apresentados a seguir:

Select count(*)
From aluno, hobby;

Select count(*)
From aluno A
Join hobby B
On A.cod_hobby = B.cod_hobby;

Select count(*)
From aluno A
Left Join hobby B
On A.cod_hobby = B.cod_hobby;

Select count(*)
From aluno A
Right Join hobby B
On A.cod_hobby = B.cod_hobby;

Select count(*)
From aluno A
Full outer Join hobby B
On A.cod_hobby = B.cod_hobby;