HQL:在查询中有条件地计数子集合
HQL:在查询中有条件地计数子集合
提问于 2014-10-02 22:04:35
对于HQL，我相当缺乏经验，所以我想知道是否有人能帮我解决这个问题。我有一个学生和StudentCollege有OneToMany关系的关系。我正在尝试编写一个查询，查找每个提出申请的学生，以及他们提交了多少个申请。我编写了下面的查询，但我不确定它是否接近我应该做的事情。
select distinct new ReportVO (stu.id, stu.first_name, stu.last_name, stu.year, stu.school.school_name, sum(case when si.applied = 1 then 1 else 0 end) as numApplications) " +
"from StudentCollege as si join si.student as stu where stu.year <= 12 and stu.user.id = :userId and si.applied = 1 order by stu.last_name当它运行时，将引发以下异常：
org.hibernate.hql.ast.QuerySyntaxException: Unable to locate appropriate constructor on class [package.location.ReportVO] [select distinct new ReportVO (stu.id, stu.first_name, stu.last_name, stu.year, stu.school.school_name, sum(case when si.applied = 1 then 1 else 0 end) as numApplications) from package.location.StudentCollege as si join si.student as stu where stu.year <= 12 and stu.user.id = :userId and si.applied = 1 order by stu.last_name]但是，我有一个VO对象的构造函数，它接受相同数量的参数，因此我认为从sum返回的类型是不正确的。我也尝试用numApplications替换Integer和Count，但是也会引发相同的异常。
public ReportVO(int id, String firstName, String lastName, int year, String school, Integer numApplications)任何帮助都是非常感谢的！
回答 1
Stack Overflow用户
发布于 2014-10-02 23:00:24
我相信您在where子句之后缺少了一个“组by”子句。
select distinct new ReportVO (stu.id, stu.first_name, stu.last_name, stu.year, stu.school.school_name, sum(case when si.applied = 1 then 1 else 0 end) as numApplications) " +
"from StudentCollege as si join si.student as stu where stu.year <= 12 and stu.user.id = :userId and si.applied = 1 group by stu.id, stu.first_name, stu.last_name, stu.year, stu.school.school_name order by stu.last_name页面原文内容由Stack Overflow提供。腾讯云小微IT领域专用引擎提供翻译支持
原文链接：
https://stackoverflow.com/questions/26170370
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