ChatGPT解决这个技术问题 Extra ChatGPT

How do you do a limit query in JPQL or HQL?

In Hibernate 3, is there a way to do the equivalent of the following MySQL limit in HQL?

select * from a_table order by a_table_column desc limit 0, 20;

I don't want to use setMaxResults if possible. This definitely was possible in the older version of Hibernate/HQL, but it seems to have disappeared.

I am using Hibernate-5.0.12. Is this still not available? It would be really heavy to get a million or so records and then apply the filter on it- setMaxResults over it as noticed by @Rachel in the answer by @skaffman.

s
skaffman

This was posted on the Hibernate forum a few years back when asked about why this worked in Hibernate 2 but not in Hibernate 3:

Limit was never a supported clause in HQL. You are meant to use setMaxResults().

So if it worked in Hibernate 2, it seems that was by coincidence, rather than by design. I think this was because the Hibernate 2 HQL parser would replace the bits of the query that it recognised as HQL, and leave the rest as it was, so you could sneak in some native SQL. Hibernate 3, however, has a proper AST HQL Parser, and it's a lot less forgiving.

I think Query.setMaxResults() really is your only option.


I would argue that Hibernate 3's approach is more correct. Your usage of Hibernate is meant to be database-agnostic, so you should have to do these sorts of things in an abstract manner.
I agree, but it makes migration is royal pain in the ass when features are dropped like that.
but with setMaxResults, first query is run and then on the resultset you call setMaxResults which would take limited number of result rows from resultset and display it to the user, in my case i have 3 million records which are queried and then am calling setMaxResults to set 50 records but i do not want to do that, while query itself i want to query for 50 records, is there a way to do that?
Old post I know. I fully agree with Rachel. Using NHibernate (.Net port of Hibernate), I've recently upgraded from 2 to 3 and same thing, top X is now throwing a parser error. However, when I added setMaxResults on the query, it did generate a TOP X in the resulting SQL (using MsSql2008Dialect). This is good.
@Rachel With setMaxResults hibernate will append the limit part to the query. It will not get all the results. You can check the query it produces by enabling: <property name="show_sql">true</property>
J
Jessu
 // SQL: SELECT * FROM table LIMIT start, maxRows;

Query q = session.createQuery("FROM table");
q.setFirstResult(start);
q.setMaxResults(maxRows);

I like this one best because setFirstResult is actually mentioned in this answer whereas here and elsewhere they just say setMaxResults this and setMaxResults that without mentioning how to set the offset.
p
pjp

If you don't want to use setMaxResults() on the Query object then you could always revert back to using normal SQL.


That's not really all that exciting.
I don't find HQL exciting either. Why not write a view on your DB server that applies the limit and then get HQL to look at that view :P
It's just one of those things, while SQL is much easier than HQL for each query, creating views and writing native SQL tends to be not so great for refactoring. I try to avoid it when I can. That actual real problem was the I wrote my MySQL query wrong anyways and thought setMaxResults was being weird. It wasn't.
and if you try to switch between different DBMS vendors, pain is waiting for you.
instead of using limit I used pageable to avoid the extra data
V
Vlad Mihalcea

The setFirstResult and setMaxResults Query methods

For a JPA and Hibernate Query, the setFirstResult method is the equivalent of OFFSET, and the setMaxResults method is the equivalent of LIMIT:

List<Post> posts = entityManager.createQuery("""
    select p
    from Post p
    order by p.createdOn
    """)
.setFirstResult(10)
.setMaxResults(10)
.getResultList();

The LimitHandler abstraction

The Hibernate LimitHandler defines the database-specific pagination logic, and as illustrated by the following diagram, Hibernate supports many database-specific pagination options:

https://i.stack.imgur.com/IGtD2.png

Now, depending on the underlying relational database system you are using, the above JPQL query will use the proper pagination syntax.

MySQL

SELECT p.id AS id1_0_,
       p.created_on AS created_2_0_,
       p.title AS title3_0_
FROM post p
ORDER BY p.created_on
LIMIT ?, ?

PostgreSQL

SELECT p.id AS id1_0_,
       p.created_on AS created_2_0_,
       p.title AS title3_0_
FROM post p
ORDER BY p.created_on
LIMIT ?
OFFSET ?

SQL Server

SELECT p.id AS id1_0_,
       p.created_on AS created_on2_0_,
       p.title AS title3_0_
FROM post p
ORDER BY p.created_on
OFFSET ? ROWS 
FETCH NEXT ? ROWS ONLY

Oracle

SELECT *
FROM (
    SELECT 
        row_.*, rownum rownum_
    FROM (
        SELECT 
            p.id AS id1_0_,
            p.created_on AS created_on2_0_,
            p.title AS title3_0_
        FROM post p
        ORDER BY p.created_on
    ) row_
    WHERE rownum <= ?
)
WHERE rownum_ > ?

The advantage of using setFirstResult and setMaxResults is that Hibernate can generate the database-specific pagination syntax for any supported relational databases.

And, you are not limited to JPQL queries only. You can use the setFirstResult and setMaxResults method seven for native SQL queries.

Native SQL queries

You don't have to hardcode the database-specific pagination when using native SQL queries. Hibernate can add that to your queries.

So, if you're executing this SQL query on PostgreSQL:

List<Tuple> posts = entityManager.createNativeQuery(
    SELECT
       p.id AS id,
       p.title AS title
    from post p
    ORDER BY p.created_on
    """, Tuple.class)
.setFirstResult(10)
.setMaxResults(10)
.getResultList();

Hibernate will transform it as follows:

SELECT p.id AS id,
       p.title AS title
FROM post p
ORDER BY p.created_on
LIMIT ?
OFFSET ?

Cool, right?

Beyond SQL-based pagination

Pagination is good when you can index the filtering and sorting criteria. If your pagination requirements imply dynamic filtering, it's a much better approach to use an inverted-index solution, like ElasticSearch.


Using OpenJPA, I cannot make this work for native queries in DB2. setMaxResults and setFirstResult are ignored, only the native query I'm passing is sent
L
Lluis Martinez

If you don't want to use setMaxResults, you can also use Query.scroll instead of list, and fetch the rows you desire. Useful for paging for instance.


Thanks, the accepted answer did not solve the issue for me, because setMaxResults() loads first every record in memory and then creates a sublist, which when there are hundred thousands or more records crashes the server, because it is out of memory. I could however go from a JPA typed query to a Hibernate query through QueryImpl hibernateQuery = query.unwrap(QueryImpl.class) and then I could use the scroll() method as you suggested.
At least with Oracle dialect this is not true (Hibernate uses the ROWNUM virtual column). Maybe it depends on the driver. Other DBs have the TOP function.
My query is using a join fetch. This results in the Hibernate warning "firstResult/maxResults specified with collection fetch; applying in memory". So with a join fetch, Hibernate is loading the full collection in memory. Dropping the join is no option because of performance reasons. When I use ScrollableResults, I have more control about which records are loaded in memory. I cannot load all records with a single ScrollableResults, because this also results in out of memory. I am experimenting loading multiple pages with different ScrollableResults. If this does not work, I will go with SQL.
That's weird, I've never encountered that. Yes sometimes using straight JDBC is the way to go, specially for massive/batch processes.
The @OneToMany relations are causing my issues. If somehow I could execute the Oracle aggregate function LISTAGG in Hibernate to concatenate the multiple values to a single value, then I can drop the joins and replace them by a subquery.
t
tk_

You can easily use pagination for this.

    @QueryHints({ @QueryHint(name = "org.hibernate.cacheable", value = "true") })
    @Query("select * from a_table order by a_table_column desc")
    List<String> getStringValue(Pageable pageable);

you have to pass new PageRequest(0, 1)to fetch records and from the list fetch the first record.


According to the question "I don't want to use setMaxResults if possible" you give the better solution, just putting Pageable as a parameter in the method and calling it sending "new PageRequest(0, 20)" I'm getting the first 20 records. Thanks.
s
swatisinghi

You need to write a native query, refer this.

@Query(value =
    "SELECT * FROM user_metric UM WHERE UM.user_id = :userId AND UM.metric_id = :metricId LIMIT :limit", nativeQuery = true)
List<UserMetricValue> findTopNByUserIdAndMetricId(
    @Param("userId") String userId, @Param("metricId") Long metricId,
    @Param("limit") int limit);

Thanks for adding an interface-only solution
C
Casey

String hql = "select userName from AccountInfo order by points desc 5";

This worked for me without using setmaxResults();

Just provide the max value in the last (in this case 5) without using the keyword limit. :P


Hm... not too sure about this, [citation needed] this may be an accident and could suddenly stop working in a new version of hibernate.
Please refer to official document.
This isn't working for me in Hibernate Version 5.2.12 Final
It's Not working, Doesn't support hibernate 4.x also.
X
Xingsheng

My observation is that even you have limit in the HQL (hibernate 3.x), it will be either causing parsing error or just ignored. (if you have order by + desc/asc before limit, it will be ignored, if you don't have desc/asc before limit, it will cause parsing error)


a
alexandrum

If can manage a limit in this mode

public List<ExampleModel> listExampleModel() {
    return listExampleModel(null, null);
}

public List<ExampleModel> listExampleModel(Integer first, Integer count) {
    Query tmp = getSession().createQuery("from ExampleModel");

    if (first != null)
        tmp.setFirstResult(first);
    if (count != null)
        tmp.setMaxResults(count);

    return (List<ExampleModel>)tmp.list();
}

This is a really simple code to handle a limit or a list.


D
Deep Chand Jaipur
Criteria criteria=curdSession.createCriteria(DTOCLASS.class).addOrder(Order.desc("feild_name"));
                criteria.setMaxResults(3);
                List<DTOCLASS> users = (List<DTOCLASS>) criteria.list();
for (DTOCLASS user : users) {
                System.out.println(user.getStart());
            }

B
ButchMonkey

You can use below query

NativeQuery<Object[]> query = session.createNativeQuery(select * from employee limit ?)
query.setparameter(1,1);

H
Hari Krishna

Below snippet is used to perform limit query using HQL.

Query query = session.createQuery("....");
query.setFirstResult(startPosition);
query.setMaxResults(maxRows);

You can get demo application at this link.


A
Andreas
@Query(nativeQuery = true,
       value = "select from otp u where u.email =:email order by u.dateTime desc limit 1")
public List<otp> findOtp(@Param("email") String email);