JPQL / QueryDSL: join subquery and get aliased column

Using subqueries in the join clause is not allowed. in JPQL, subqueries are only allowed in the WHERE and HAVING part. The join method signatures in Querydsl JPA queries are too wide.

As this query needs two levels of grouping, maybe it can't be expressed with JPQL / Querydsl JPA.

I'd suggest to write this query using the Querydsl JPA Native query support.

As Querydsl JPA uses JPQL internally, it is restricted by the expressiveness of JPQL.

I know that this question is old and already has an accepted answer, but judging from this question, it seems to still be troubling guys. See my answer in the same question. The use of JoinFlag in the join() section and Expression.path() is able to achieve left-joining a subquery. Hope this helps someone.