具有最大结果的 JPA 计数查询

Question

您能否分享一下通过 JPA 编写的代码 sn-p 以生成以下 sql 查询

SELECT COUNT(*) FROM Customer c 
WHERE c.countryId ='Canada' AND 
      c.lanuguage ='ENG' AND 
      ROW_NUM <=10;

因为我尝试了以下方式。但是 MaxResults 似乎没有得到应用，因​​为我可以收到超过 10 个的计数。

Query query = em.createQuery("SELECT COUNT(c) FROM Customer c where c.countryId ='Canada' and c.lanuguage ='ENG'");
query.setMaxResults(10);
long customerCount = (Long)query.getSingleResult();

Answer 1

按计数选择将始终返回单个值。如果您希望计数低于 10，请添加 HAVING。

SELECT COUNT(c) AS 
FROM Customer c
WHERE c.countryId='Canada' and c.language='END'
HAVING COUNT(c)<=10