使用SUM和COUNT的JPQL本机查询 [英] JPQL Native Query using SUM and COUNT

问题描述

我正在尝试运行以下代码:

I am trying to run the following code:

public BigDecimal valuate(String searchTerms, String categoryPath) {
    Query query = em.createNativeQuery("SELECT SUM(maxBidAmount) / COUNT(maxBidAmount) FROM Item WHERE MATCH(title) AGAINST(':searchTerms') AND categoryPath=':categoryPath'", Double.class);
    query.setParameter("searchTerms", searchTerms);
    query.setParameter("categoryPath", categoryPath);
    double value = (double) query.getSingleResult();
    return new BigDecimal(value);
}

这样做时，出现以下异常:

When I do so, I get the following exception:

Exception Description: Missing descriptor for [class java.lang.Double].

当我删除Double.class时，我得到了另一个异常.

When I remove Double.class, I get a different exception.

因此，我只是想知道将COUNT和SUM与JPQL一起使用的正确方法.

So, I'm just wondering the correct method of using COUNT and SUM with JPQL.

推荐答案

如果SQL有效，则无需在查询def中指定Double.class-只需使用em.createNativeQuery(SQLString);即可. 当您希望JPA提供程序从结果中构建实体时使用返回类型，但是在这种情况下，您需要原始数据.

IF the SQL is valid, you do not need to specify the Double.class in the query def - just use em.createNativeQuery(SQLString); The return type is used when you want the JPA provider to build an entity from the results, but in this case you want the raw data.

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