How to get the sum of a Bigdecimal column

Question

I need to add a data column BigDecimal Mysql, which has already been filtered from a given range. I am trying with SELECT SUM(preco_total) FROM venda; in the code below, but I’m not getting results.

Here are my codes:

Table structure venda:

> `DESCRIBE venda;`
+-----------------+---------------+------+-----+---------+----------------+
| Field           | Type          | Null | Key | Default | Extra          |
+-----------------+---------------+------+-----+---------+----------------+
| codigo          | bigint(20)    | NO   | PRI | NULL    | auto_increment |
| bairro          | varchar(50)   | YES  |     | NULL    |                |
| cep             | varchar(30)   | YES  |     | NULL    |                |
| cidade          | varchar(30)   | YES  |     | NULL    |                |
| complemento     | varchar(30)   | YES  |     | NULL    |                |
| estado          | varchar(2)    | YES  |     | NULL    |                |
| horario         | datetime      | NO   |     | NULL    |                |
| logradouro      | varchar(40)   | YES  |     | NULL    |                |
| nome_cliente    | varchar(80)   | YES  |     | NULL    |                |
| preco_total     | decimal(10,2) | NO   |     | NULL    |                |
| vendedor_codigo | bigint(20)    | NO   | MUL | NULL    |                |
+-----------------+---------------+------+-----+---------+----------------+
11 rows in set (0.01 sec)

My code vendaBean:

public void soma() {
        try {
            VendaDAO vendaDAO = new VendaDAO();
            vendaDAO.soma();

        } catch (RuntimeException erro) {
            Messages.addGlobalError("Não foi possível exibir a soma. Contate o Suporte.");
        }
    }

}

Below is my code vendaDAO;

public List<Venda> soma() {
        List<Venda> vendas = null;
        Session sessao = HibernateUtil.getFabricaDeSessoes().openSession();
        try {
            StringBuilder sql = new StringBuilder();
            sql.append("SELECT SUM(preco_total) FROM venda ");

        } catch (RuntimeException erro) {
            throw erro;
        } finally {
            sessao.close();
        }
        return vendas;
    }

}

And finally my code venda.xhtml:

<p:outputLabel value="Total: R$" />
                <h:outputText value="#{vendaBean.soma()}">
                    <f:convertNumber locale="pt_BR"                     minFractionDigits="2" />
                </h:outputText>