/*
    使用jpql查询，统计客户的总数
        sql：select count(cust_id) from cst_customer
        spql:select count(custId) from Customer
     */
    @Test
    public void testCount(){
        EntityManager entityManager = JpaUtils.getEntityManager();
        EntityTransaction tx = entityManager.getTransaction();
        tx.begin();

        //查询全部
        //根据jpql语句创建Query查询对象
        String jpql = "select count(custId) from Customer";
        Query query = entityManager.createQuery(jpql);

        //对参数进行赋值
        //发送查询，并封装结果
        /*
        getResultList: 直接将查询结果封装为List集合
        getSingleResult：得到唯一的结果集
         */
        Object singleResult = query.getSingleResult();
        System.out.println(singleResult);


        tx.commit();
        entityManager.close();

    }