Duvida simples em SQL junção

CREATE TABLE aluno
(
        id_aluno integer,
	nome_aluno varchar (30)
)
WITH (
  OIDS=FALSE
);
ALTER TABLE aluno
  OWNER TO postgres;

CREATE TABLE materia
(
        id_materia integer,
	nome_materia varchar (30)
)
WITH (
  OIDS=FALSE
);
ALTER TABLE aluno
  OWNER TO postgres;

CREATE TABLE AluMat
(
	id_aluno integer,
        id_materia integer
	
)
WITH (
  OIDS=FALSE
);
ALTER TABLE aluno
  OWNER TO postgres;

  alter table aluno add constraint "pkAluno" primary key ("id_aluno");

  alter table materia add constraint "pkMateria" primary key ("id_materia");

  alter table AluMat add constraint "fkAluMatAluno"
	foreign key ("id_aluno") REFERENCES aluno("id_aluno");

  alter table AluMat add constraint "fkAluMatMateria"
	foreign key ("id_materia") REFERENCES materia("id_materia");




Select A.nome_aluno,A.id_aluno,M.nome_materia
From aluno A, Materia M
Where (A.id_aluno = A.nome_aluno = 'Jose') AND (A.id_aluno = M.nome_materia = 'Matematica');