Question

我在MySQL数据库中有两个表。

产品
order_item

客户下达存储在order_item表格中的产品订单 - 从product到order_item的一对多关系。

目前，我正在执行以下查询。

SELECT t0.prod_id, 
       sum(t1.quantity_ordered) 
FROM   projectdb.product t0, 
       projectdb.order_item t1 
WHERE  (t0.prod_id = t1.prod_id) 
GROUP  BY t0.prod_id 
HAVING (sum(t1.quantity_ordered) >= ?) 
ORDER  BY sum(t1.quantity_ordered) DESC

生成此SQL的Criteria查询如下所示。

CriteriaBuilder criteriaBuilder=entityManager.getCriteriaBuilder();
CriteriaQuery<Object[]>criteriaQuery=criteriaBuilder.createQuery(Object[].class);
Metamodel metamodel = entityManager.getMetamodel();
Root<OrderItem> root = criteriaQuery.from(metamodel.entity(OrderItem.class));

Join<OrderItem, Product> orderItemProdJoin = root.join(OrderItem_.prodId, JoinType.INNER);

List<Expression<?>>expressions=new ArrayList<Expression<?>>();
expressions.add(orderItemProdJoin.get(Product_.prodId));
expressions.add(criteriaBuilder.sum(root.get(OrderItem_.quantityOrdered)));
criteriaQuery.multiselect(expressions.toArray(new Expression[0]));

criteriaQuery.groupBy(orderItemProdJoin.get(Product_.prodId));
criteriaQuery.having(criteriaBuilder.greaterThanOrEqualTo(criteriaBuilder.sum(root.get(OrderItem_.quantityOrdered)), criteriaBuilder.literal(5)));

criteriaQuery.orderBy(criteriaBuilder.desc(criteriaBuilder.sum(root.get(OrderItem_.quantityOrdered))));
List<Object[]> list = entityManager.createQuery(criteriaQuery).getResultList();

此查询汇总了order_item表中每组产品的数量。

它显示的行列表如下所示。

prod_id       qunatity_ordered

 6            11
 8             8
26             8
 7             7
31             7
12             6
27             6
24             5
 9             5

是否可以只计算此查询生成的行数 - 在这种情况下为9？

我正在使用EclipseLink 2.5.2和Hibernate 4.3.6 final提供的JPA 2.1。

Answer 1

您有两种选择：

SELECT COUNT(*)
  FROM (
   SELECT 1, 
     FROM projectdb.product t0, 
          projectdb.order_item t1 
    WHERE (t0.prod_id = t1.prod_id) /* I prefer not to use Implicit Joins */
 GROUP BY t0.prod_id 
   HAVING (sum(t1.quantity_ordered) >= ?) 
       ) groups

OR：

list.size();

Answer 2

计算此类行的一种方法是将给定查询包装在另一个计算行的查询中，并使给定查询成为子查询，如下所示。

SELECT count(DISTINCT(t0.prod_id)) 
FROM   projectdb.product t0 
WHERE  EXISTS (SELECT t1.prod_id 
               FROM   projectdb.order_item t2, 
                      projectdb.product t1 
               WHERE  ((t1.prod_id = t0.prod_id ) 
                        AND ( t1.prod_id = t2.prod_id)) 
               GROUP  BY t1.prod_id 
               HAVING (sum(t2.quantity_ordered) >= ?))

生成上述SQL的条件查询。

CriteriaBuilder criteriaBuilder=entityManager.getCriteriaBuilder();
CriteriaQuery<Long>criteriaQuery=criteriaBuilder.createQuery(Long.class);
Metamodel metamodel = entityManager.getMetamodel();
Root<Product> root = criteriaQuery.from(metamodel.entity(Product.class));
criteriaQuery.select(criteriaBuilder.countDistinct(root));

Subquery<Long> orderItemSubquery = criteriaQuery.subquery(Long.class);
Root<OrderItem> orderItemRoot = orderItemSubquery.from(metamodel.entity(OrderItem.class));
Join<OrderItem, Product> orderItemProdJoin = orderItemRoot.join(OrderItem_.prodId, JoinType.INNER);

orderItemSubquery.select(orderItemProdJoin.get(Product_.prodId));
orderItemSubquery.where(criteriaBuilder.equal(root, orderItemRoot.get(OrderItem_.prodId)));
orderItemSubquery.groupBy(orderItemProdJoin.get(Product_.prodId));
orderItemSubquery.having(criteriaBuilder.greaterThanOrEqualTo(criteriaBuilder.sum(orderItemRoot.get(OrderItem_.quantityOrdered)), criteriaBuilder.literal(5)));
criteriaQuery.where(criteriaBuilder.exists(orderItemSubquery));

Long count = entityManager.createQuery(criteriaQuery).getSingleResult();
System.out.println("count = "+count);

我通常避免使用IN()子查询并使用EXISTS()子查询。不过，可以使用IN()重写相同的查询，如下所示。

SELECT count(DISTINCT(t0.prod_id)) 
FROM   projectdb.product t0 
WHERE  t0.prod_id IN (SELECT t1.prod_id 
                      FROM   projectdb.order_item t2, 
                             projectdb.product t1 
                      WHERE  (t1.prod_id = t2.prod_id) 
                      GROUP  BY t1.prod_id 
                      HAVING (sum(t2.quantity_ordered) >= ?))

相应的标准查询。

CriteriaBuilder criteriaBuilder=entityManager.getCriteriaBuilder();
CriteriaQuery<Long>criteriaQuery=criteriaBuilder.createQuery(Long.class);
Metamodel metamodel = entityManager.getMetamodel();
Root<Product> root = criteriaQuery.from(metamodel.entity(Product.class));
criteriaQuery.select(criteriaBuilder.countDistinct(root));

Subquery<Long> orderItemSubquery = criteriaQuery.subquery(Long.class);
Root<OrderItem> orderItemRoot = orderItemSubquery.from(metamodel.entity(OrderItem.class));
Join<OrderItem, Product> orderItemProdJoin = orderItemRoot.join(OrderItem_.prodId, JoinType.INNER);

orderItemSubquery.select(orderItemProdJoin.get(Product_.prodId));
orderItemSubquery.groupBy(orderItemProdJoin.get(Product_.prodId));
orderItemSubquery.having(criteriaBuilder.greaterThanOrEqualTo(criteriaBuilder.sum(orderItemRoot.get(OrderItem_.quantityOrdered)), criteriaBuilder.literal(5)));
criteriaQuery.where(criteriaBuilder.in(root.get(Product_.prodId)).value(orderItemSubquery));

Long count = entityManager.createQuery(criteriaQuery).getSingleResult();
System.out.println("count = "+count);

关于ORM的限制，我找不到比这更好的选择。

使用＆＃34; group by＆＃34;计算过滤的行数。并且＆＃34;有＆＃34;在JPA

2 个答案: