JPQL select query, unable to Group By

Question

after hours I don't seem to find a way to achieve this, I have 2 entities:

public class Price{
@Id
int id;

@Temporal(TemporalType.DATE)
private Date dtComu;

private String descCarb;

private Double price;

//bi-directional many-to-one association to Distributor
@ManyToOne
@JoinColumn(name="idImpiant")
private Distributor distributor;

AND

public class Distributor{

@Id
private int idImpiant;

private String province;

//bi-directional many-to-one association to Price
@OneToMany(mappedBy="distributor")
private List<Price> prices;

What I need to do seems pretty simple, for each distributor, get the latest price. What i thought was to get a list of Prices(each price with have a distributor), order by date and group by distributor. My query is:

SELECT e FROM Price e JOIN e.distributor d WHERE e.descCarb like '%Diesel%' group by e.distributor order by e.dtComu desc

The error i get is:

SELECT list is not in GROUP BY clause and contains nonaggregated column 'price0_.id' which is not functionally dependent on columns in GROUP BY clause

is there another way i haven't thought to achieve this?

Answer 1

The error you see is stemming from that it is not clear which entity you want per distributor group. Here is one way to do this using HQL:

select e FROM Price e JOIN e.distributor d
where e.descCarb like '%Diesel%' and
      e.dtComu = (select max(ee.dtComu) from Price ee where ee.distributor = e.distributor)

This uses a correlated subquery to check that the matching Price entity is the latest one for each distributor.