如何基于字段查询具有单个子对象的表中的对象的sql？

Question

我现在拥有的是：

与所有社区等获得List<Town>：

(Town) em.createQuery(from Town towns"
        + " left join fetch towns.neighborhoods neighborhood"
        + " left join fetch neighborhood.population population"
        + " left join fetch population.age age"
        + " where age.value = :ageValue")
       .setParameter("ageValue", ageValue)

我希望得到一个List<Town>只有一个邻居，这是neighborhood.creationDate的第一个。

我怎么做 ？

我不想把它们全部拿走然后删除它。

谢谢。

Answer 1

我建议在where子句中添加一个子查询，如下所示：

where age.value = :ageValue 
    AND neighborhood.creationDate = 
         (Select max(nh.creationDate) From Neighborhood nh 
               where nh.townsId = towns.townsId)