Question

我想使用此SQL查询来实现JPA查询：

String hql = "SELECT DATE(date) AS Date, SUM(volume) AS amount, COUNT(*) AS number_of_transactions " + 
                " FROM " + PaymentTransactionsDailyFacts.class.getName() + " WHERE (date BETWEEN :start_date AND :end_date )" + 
                " GROUP BY DATE(date)";

我尝试过：

String hql = "SELECT DATE(e.date) AS Date, SUM(e.volume) AS amount, COUNT(e.*) AS count " + 
                " FROM " + PaymentTransactionsDailyFacts.class.getName() + " e WHERE (date BETWEEN :start_date AND :end_date )" + 
                " GROUP BY DATE(date)";

但是我得到了错误：

expecting IDENT, found '*' near line 1, column 63 [SELECT DATE(e.date) AS Date, SUM(e.volume) AS amount, COUNT(e.*) AS count  FROM .......PaymentTransactionsDailyFacts e WHERE (date BETWEEN :start_date AND :end_date ) GROUP BY DATE(date)]

将查询执行到JPA中的正确方法是什么？

Answer 1

JPQL不知道*是什么意思。相反，您只会说e，而不是e.*。

String hql = "SELECT DATE(e.date) AS Date, SUM(e.volume) AS amount, COUNT(e) AS count " 
              + " FROM " + PaymentTransactionsDailyFacts.class.getName()
              + " e WHERE (date BETWEEN :start_date AND :end_date )" 
              + " GROUP BY DATE(date)";

这是因为JPQL在 Java 实体上运行。请注意，您是从类名而不是表中说的。对象没有通配符，表明类中的任何字段。相反，您指定对象本身不为null表示存在一行。

SQL中的e.*语法实质上是（尽管可能不是字面意思）说该行上至少存在一个非空列。因为它没有任何直接的方式来表示存在行。但是JPQL确实有办法说一个对象存在。那是基本的Java非空检查。因此，在JPQL中，您可以使用Java方式（尽管采用JPQL语法）而不是SQL方式。

另请参见

使用COUNT和SUM实施JPA查询

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