Hibernate HQL内部联接子选择

Question

I got the following SQL which I wanted to transform into valid HQL. The issue with this is, that its not permitted to join on a sub-query per the docs . Even though these are old docs (v3.3) this section still seems to still hold in hibernate 5.3.

SELECT f.date,
    f.name,
    SUM(f.seats) 
FROM Foo f 
        INNER JOIN (SELECT fl.date,
                        fl.start + fl.end AS code 
                    FROM Foo fl 
                    WHERE fl.date >= (SELECT MAX(earliestDate) 
                                            FROM Bar) 
                        AND fl.name = :name) fl 
        ON f.start + f.end = code 
        AND f.date = fl.date 
WHERE f.date >= (   SELECT MAX(earliestDate) 
                        FROM Bar)   
GROUP BY f.date,
    f.name 
ORDER BY f.date ASC,
    SUM(f.seats) DESC

I came up with this HQL:

SELECT NEW com.company.project.model.FooRepresentation( f.fooId.date,
    f.fooId.name,
    SUM(f.seats)) 
FROM Foo f 
        INNER JOIN (SELECT fl.fooId.date,
                        fl.fooId.start + fl.fooId.end AS code 
                    FROM Foo fl 
                    WHERE fl.fooId.date >= (SELECT MAX(earliestDate) 
                                            FROM FooConfig) 
                        AND fl.fooId.name = :name) fl 
        ON f.fooId.start + f.fooId.end = code 
        AND f.fooId.date = fl.fooId.date 
WHERE f.fooId.date >= ( SELECT MAX(earliestDate) 
                        FROM FooConfig) 
GROUP BY f.fooId.date,
    f.fooId.name 
ORDER BY f.fooId.date ASC,
    SUM(f.seats) DESC

Trying to execute this HQL query, results in this exception

org.hibernate.hql.internal.ast.QuerySyntaxException: unexpected token: ( near line 1, column 169

which hints to the ( at INNER JOIN (SELECT .

Is there a way to join on sub-queries within HQL? If not, what would be the best way to achieve the same results as the SQL with HQL?

---

I am not that good with converting the inner join on <sub-query> to an actual where clause where the sub-query is permitted

Answer 1

I think your SQL query can be rewritten to this:

SELECT f.date, f.name, SUM(f.seats) 
FROM Foo f 
WHERE EXISTS (
  SELECT 1
  FROM Foo f1
  WHERE f.start + f.end = f1.start + f1.end
  AND f.date = f1.date
  AND f1.date >= (SELECT MAX(earliestDate) FROM Bar)
  AND f1.name = :name  
)
AND f.date >= (SELECT MAX(earliestDate) FROM Bar)
GROUP BY f.date, f.name
ORDER BY f.date ASC, SUM(f.seats) DESC

This should be simpler to translate to HQL, and it might even be more correct, because your original query seems to create an unwanted cartesian product between the self joined rows.

There's probably an even better way to query this in SQL, without self joining the Foo table, using a single pass through the table. But I'd need to know more about your real world use-case for that, and what RDBMS you're using.

Answer 2

With the help of @LukasEder's answer, I created this HQL:

SELECT NEW com.company.project.model.FooRepresentation( f.fooId.date,
    f.fooId.name,
    SUM(f.seats) ) 
FROM Foo f 
WHERE EXISTS (  SELECT 1 
                FROM Foo f1 
                WHERE f.fooId.start + f.fooId.end = f1.fooId.start + f1.fooId.end 
                    AND f.fooId.date = f1.fooId.date 
                    AND f1.fooId.date >= (  SELECT MAX(earliestDate) 
                                            FROM FooConfig) 
                    AND f1.fooId.name = :name ) 
    AND f.fooId.date >= (   SELECT MAX(earliestDate) 
                            FROM FooConfig) 
GROUP BY f.fooId.date,
    f.fooId.name 
ORDER BY f.fooId.date ASC,
    SUM(f.seats) DESC

Previously I was running this native SQL query with a ResultTransformer :

SELECT f.date,
    f.name,
    SUM(f.seats) 
FROM Foo f 
        INNER JOIN (SELECT fl.date,
                        fl.start + fl.end AS code 
                    FROM Foo fl 
                    WHERE fl.date >= (  SELECT MAX(earliestDate) 
                                        FROM FooConfig) 
                        AND fl.name = :name) fl 
        ON f.start + f.end = code 
        AND f.date = fl.date 
WHERE f.date >= (   SELECT MAX(earliestDate) 
                    FROM FooConfig) 
GROUP BY f.date,
    f.name 
ORDER BY f.date ASC,
    SUM(f.seats) DESC

there are actually slight differences with the results between the two queries, but those are not consistent. With consistent I mean in this case, that its not for every possible date that the results differ, just for some. Also for the provided parameter :name , the results are consistent. I will evaluate more on which results are more fitting, but I wouldn't be surprised if the new ones are correct.