I already resolved my problem. This procedure return a value.

Can I execute a procedure that return a value without getting this
value? Or I must provide a variable to receive the value of the
returning?

> execute procedure INSERIR_ALUNOS_EM_DIARIO(new.ID_CURSO,
> new.ID_DISCIPLINA,
> new.ID_FASE,
> new.ID_TURMA);
> --------------