使用条件和/或投影（子查询）将SQL转换为休眠查询

Question

Could anyone please help to convert this SQL Query to HQL (using criteria and projection) to have in result Set<topic> topics .

SELECT t.id, t.title, COUNT(p.id) as count, MAX(p.created_on) as `latest`
FROM topics t
JOIN posts p
  ON t.id = p.topic_id
GROUP BY t.id
ORDER BY count ASC;

My problem is that Hibernate is fetching all data connected to one of columns of the topic table (connected table is users ) - and query takes to much time and unnecessary selects and joins.
Tried to use projections but couldn't.
Thanks in advance for any help!

Answer 1

From your code,

SELECT t.id, t.title, COUNT(p.id) as count, MAX(p.created_on) as `latest`
FROM topics t
JOIN posts p
  ON t.id = p.topic_id
GROUP BY t.id
ORDER BY count ASC;

You can remove JOIN and convert it in WHERE condition. Hope it will save you.

Use this following code

SELECT t.id, t.title, COUNT(p.id) as count, MAX(p.created_on) as `latest`
FROM topics t, posts p
WHERE t.id = p.topic_id
GROUP BY t.id
ORDER BY count ASC;