HQL / SQL根据计数选择前10条记录

Question

我有2张桌子：

CATEGORY (id)
POSTING (id, categoryId)

我正在尝试编写HQL或SQL查询来查找发布次数最多的前10个类别。

感谢帮助。

Answer 1

SQL查询：

SELECT  c.Id, sub.POSTINGCOUNT
FROM CATEGORY c where c.Id IN
( 
    SELECT TOP 10 p.categoryId
    FROM POSTING p
    GROUP BY p.categoryId 
    order by count(1) desc
)

总部：

Session.CreateQuery("select c.Id
        FROM CATEGORY c where c.Id IN
        ( 
            SELECT  p.categoryId
            FROM POSTING p
            GROUP BY p.categoryId 
            order by count(1) desc
        )").SetMaxResults(10).List();

http://sqlinthewild.co.za/index.php/2010/01/12/in-vs-inner-join/

Answer 2

在 SQL 中你可以这样做：

SELECT c.Id, sub.POSTINGCOUNT
FROM CATEGORY c 
INNER JOIN 
( 
    SELECT p.categoryId, COUNT(id) AS 'POSTINGCOUNT'
    FROM POSTING p
    GROUP BY p.categoryId
) sub ON c.Id = sub.categoryId
ORDER BY POSTINGCOUNT DESC
LIMIT 10