row_number() over partition in hql

Question

What is the equivalent of row_number() over partition in hql I have the following query in hql:

select s.Companyname, p.P         


        

Answer 1

Row number by partition looks like this:

row_number() over (partition by s.Companyname)

You can not use window function row_number in where clause, so you have to do subquery with filter by its value:

select * from (
  -- here is your query
  select 
    ...,
    row_number() over (partition by s.Companyname) as rowNum
  from ...
  where ...
) as res
where rowNum <= n

Answer 2

As far as I know you cannot use row_number() neither in HQL nor in JPQL. I propose to use a native SQL query in this case:

@PersistenceContext
protected EntityManager entityManager;
...

    String sQuery = "SELECT q.* FROM (" +
            "SELECT s.company_name, " +
               "p.product_name, " +
               "sum(od.unit_price * od.quantity - od.discount) as SalesAmount, " +
               "row_number() OVER (partition by s.company_name) as rn " +
            "FROM OrderDetails od " +
            "INNER JOIN Orders o ON o.id = od.order_id " +
            "INNER JOIN Products p ON p.id = od.product_id " +
            "INNER JOIN Suppliers s ON s.id = p.supplier_id " +
            "WHERE o.order_date between '2010/01/01' and '2014/01/01') as q " +
        "WHERE rn <= :n";

    List<ResultDbo> results = new ArrayList<>();
    Query query = entityManager.createNativeQuery(sQuery);
    query.setParameter("n", n);
    List<Object[]> resultSet = query.getResultList();
    for (Object[] resultItem : resultSet) {
        ResultDbo result = new ResultDbo();
        result.setCompanyName((String) resultItem[0]);
        result.setProductName((String) resultItem[1]);
        result.setSalesAmount((String) resultItem[2]);
        results.add(result);
    }

If you ever try to use OVER() in HQL you'll almost certainly get some validation exception like java.lang.IllegalArgumentException: org.hibernate.hql.internal.ast.QuerySyntaxException: unexpected token: OVER near line 1, column 42 ...