#1005 - Can't create table 'classorganizer.turma' (errno: 150) - mysql

Question

I keep getting the following error: *#1005 - Can't create table 'classorganizer.turma' (errno: 150) (Detalhes...) *
from trying to create the table Turma although I've double checked all the foreign keys cases in that class. Does anyone knows whats wrong?
Thank you!
CREATE TABLE Usuario(
email VARCHAR(50) NOT NULL,
nome VARCHAR(30),
senha INTEGER NOT NULL,
dataCadastro DATE NOT NULL,
CONSTRAINT pkUsu PRIMARY KEY(email),
CONSTRAINT formatoEmail CHECK(email LIKE '%#%.%')
)ENGINE=InnoDB;
CREATE TABLE Professor(
id INTEGER NOT NULL AUTO_INCREMENT,
nome VARCHAR(30) NOT NULL UNIQUE,
ranking INTEGER DEFAULT 3,
usuario VARCHAR(50) NOT NULL,
CONSTRAINT pk_prof PRIMARY KEY (id),
CONSTRAINT fk_usu FOREIGN KEY (usuario) REFERENCES Usuario(email) ON DELETE CASCADE ON UPDATE CASCADE,
CONSTRAINT limites_rank CHECK(ranking >0 AND ranking<6)
)ENGINE=InnoDB;
CREATE TABLE Materia(
codigo VARCHAR(8) NOT NULL,
nro_turmas INTEGER DEFAULT 0,
nome VARCHAR(20) NOT NULL UNIQUE,
nro_cred_aula INTEGER DEFAULT 0,
nro_cred_trab INTEGER DEFAULT 0,
prioridade INTEGER DEFAULT 3,
usuario VARCHAR(50) NOT NULL,
CONSTRAINT pk_prof PRIMARY KEY (id),
CONSTRAINT fk_usu FOREIGN KEY (usuario) REFERENCES Usuario(email) ON DELETE CASCADE ON UPDATE CASCADE,
CONSTRAINT limites_prio CHECK(prioridade >0 AND prioridade<6)
)ENGINE=InnoDB;
CREATE TABLE Turma(
nro INTEGER NOT NULL AUTO_INCREMENT,
prioridade INTEGER DEFAULT 3,
materia VARCHAR(8) NOT NULL,
professor INTEGER NOT NULL,
usuario VARCHAR(50) NOT NULL,
CONSTRAINT pk_turma PRIMARY KEY (nro),
CONSTRAINT fk_mat FOREIGN KEY (materia) REFERENCES Materia(codigo) ON DELETE CASCADE ON UPDATE CASCADE,
CONSTRAINT fk_prof FOREIGN KEY (professor) REFERENCES Professor(id) ON DELETE SET NULL ON UPDATE CASCADE,
CONSTRAINT fk_usu FOREIGN KEY (usuario) REFERENCES Usuario(email) ON DELETE CASCADE ON UPDATE CASCADE,
CONSTRAINT limites_prio CHECK(prioridade >0 AND prioridade<6)
)ENGINE=InnoDB;

Answer 1

There are lots of errors.
CONSTRAINT pk_prof PRIMARY KEY (id). id column doesn't exist in table Materia.
Constraint names (pk_prof, fk_usu) are already used in Professor table. You have used it in both Materia and Turma table.
Correct it by choosing unique names. Easiest way is to omit the name. MySQL handle it.
codigo column of Materia is referenced in Turma table, But its not a *key.*
professor column of Turma is defined to be NOT NULL. But you used ON DELETE SET NULL.