包含嵌套聚合函数的Hibernate HQL查询有问题

Question

以下hql_query String按预期工作并传递数据记录。它给出了一个列表列表，其中嵌套列表由一个人和“persAccsBOs的数量”组成。

hql_query_string = ""
+ "select distinct pers, count(persAccsBOs) as anzBo from Person as pers"
+ " inner join pers.personenAttribute as persAttr inner join persAttr.pa_pk.attribut as pAttr"
+ " inner join pers.accounts as persAccs"
+ " inner join persAccs.berechtigungsobjekte as persAccsBOs"
+ " where pAttr.name='UID_Department'"
+ " and persAttr.wert='Sales (10100200)'"
+ " group by pers";

现在，我想要实现和失败的是获得所有anzBo的平均值。我尝试了以下query_string：

query_string = ""
+ "select avg(anzBo) from "
+ " (select distinct pers, count(persAccsBOs) as anzBo from Person as pers"
+ " inner join pers.personenAttribute as persAttr inner join persAttr.pa_pk.attribut as pAttr"
+ " inner join pers.accounts as persAccs"
+ " inner join persAccs.berechtigungsobjekte as persAccsBOs"
+ " where pAttr.name='UID_Department'"
+ " and persAttr.wert='Sales (10100200)'"
+ " group by pers)";

我收到错误消息：

  

意外令牌：选择第1行第25列附近[select avg（anzBo）   来自select distinct pers ...

我希望你知道我想做什么。你能帮我组建正确的hql_string吗？

更新：

如果我试试这个：

query_string = ""
+ "select distinct pers, count(persAccsBOs) as anzBo, avg(anzBo) from Person as pers"
+ " inner join pers.personenAttribute as persAttr inner join persAttr.pa_pk.attribut as pAttr"
+ " inner join pers.accounts as persAccs"
+ " inner join persAccs.berechtigungsobjekte as persAccsBOs"
+ " where pAttr.name='UID_Department'"
+ " and persAttr.wert='Sales (10100200)'"
+ " group by pers";

我将得到一个java.lang.NullPointerException。