> For the complete documentation index, see [llms.txt](https://heunnajo.gitbook.io/jpa-basic/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://heunnajo.gitbook.io/jpa-basic/11.-2/undefined-1.md).

# 다형성 쿼리

TYPE

* 조회 대상을 특정 자식으로 한정\
  ex) Item 중에 Book, Movie를 조회할 때
* JPQL

```sql
select i from Item i

where type(i) IN (Book, Movie)
```

* SQL

```sql
select i from i

where i.DTYPE in (‘B’, ‘M’)
```

TREAT

* 자바의 타입 캐스팅과 유사
* 상속 구조에서 부모 타입을 특정 자식 타입으로 다룰 때 사용\
  \=>부모 클래스를 자식 클래스로 다운캐스팅 가능!
* FROM, WHERE, SELECT(하이버네이트 지원) 사용
* JPQL

```sql
select i from Item i
where treat(i as Book).auther = 'kim'
```

* SQL

```sql
select i.* from Item i
where i.DTYPE = 'B' and i.auther = 'kim'
```


---

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