This document discusses JPQL join fetch queries in JPA. It explains that join fetch queries can result in a cartesian product between tables if not written properly. It provides examples of order, member, and delivery entities to illustrate this issue. It also discusses using the distinct keyword in JPQL queries, clarifying that distinct applies to root entities, not rows in the SQL query. Finally, it mentions that fetch joins can be optimized using batch fetching.

1. JPA
Covenant
Chapter 5
JPA
JPQL Join Fetch

2. - Name. Covenant Ko
- Company. 11번가
- Github 용감한친구들 Organization Founder & Maintainer. https://github.com/brave-people
- Github. https://github.com/KoEonYack
- Tech Blog. https://covenant.tistory.com/ (누적 방문 51만)

3. (Cartesian Product)
JPQL Fetch Join ?
https://www.mathstopia.net/sets/cartesian-product
A×B = { (a,b) | aϵA and bϵB }
Cartesian Product is the multiplication of two sets to
form the set of all ordered pairs.

4. (Cartesian Product)
JPQL Fetch Join ?

5. 1
1
1 *
1
*

6. 1
1
1 *
1
*

7. 1
1
1 *
1
*

8. 1
1
1 *
1
*
Order Member Delivery

9. 1
1
1 *
1
*
Order Member Delivery
?

10. 1
1
1 *
1
*
Order Member Delivery
?
.

11. 1
* 1
1
1
* *
1

12. 1
* 1
1
1
* *
1
DB Order 2 OrderItem 2 ?
OrderA
OrderA
OrderB
OrderB
OrderItemA
OrderItemB
OrderItemA
OrderItemB

13. Distinct
1. SQL distinct row .
2. JPQL distinct Root Entity

14. Distinct
1. SQL distinct row .
2. JPQL distinct Root Entity
? No

15. Distinct
1. SQL distinct row .
2. JPQL distinct Root Entity
?

16. Distinct
1. SQL distinct row .
2. JPQL distinct Root Entity
? No

17. Distinct
1. SQL distinct row .
2. JPQL distinct Root Entity
? No

18. ?
https://velog.io/@neity16/

19. ?
https://velog.io/@neity16/
DB JPQL DISTINCT

20. 1. ToOne(OneToOne, ManyToOne)
2.
3. hibernate default_batch_fetch_size or @BatchSize

21. JPA
Covenant
Chapter 5
JPA
JPQL Join Fetch