집합 산술 연산자¶

SET, MULTISET, LIST¶

컬렉션 타입(SET, MULTISET, LIST (= SEQUENCE)) 데이터에 대해 합집합, 차집합, 교집합을 구하기 위해서 각각 +, -, * 연산자를 사용할 수 있다.

```<value_expression>  <set_arithmetic_operator> <value_expression>

<value_expression> ::=
collection_value |
NULL

<set_arithmetic_operator> ::=
+ (합집합) |
- (차집합) |
* (교집합)
```

다음은 컬렉션 타입이 피연산자인 경우, 연산별 결과 데이터 타입을 나타낸 표이다.

피연산자의 타입별 결과 데이터 타입

SET MULTISET LIST
SET + , - , * : SET + , - , * : MULTISET + , - , * : MULTISET
MULTISET + , - , * : MULTISET + , - , * : MULTISET + , - , * : MULTISET
LIST (=SEQUENCE) +, -, * : MULTISET +, -, * : MULTISET + : LIST -, * : MULTISET

다음은 컬렉션 타입을 가지고 산술 연산을 수행하는 예이다.

```SELECT ((CAST ({3,3,3,2,2,1} AS SET))+(CAST ({4,3,3,2} AS MULTISET)));
```
``` (( cast({3, 3, 3, 2, 2, 1} as set))+( cast({4, 3, 3, 2} as multiset)))
======================
{1, 2, 2, 3, 3, 3, 4}
```
```SELECT ((CAST ({3,3,3,2,2,1} AS MULTISET))+(CAST ({4,3,3,2} AS MULTISET)));
```
``` (( cast({3, 3, 3, 2, 2, 1} as multiset))+( cast({4, 3, 3, 2} as multiset)))
======================
{1, 2, 2, 2, 3, 3, 3, 3, 3, 4}
```
```SELECT ((CAST ({3,3,3,2,2,1} AS LIST))+(CAST ({4,3,3,2} AS MULTISET)));
```
``` (( cast({3, 3, 3, 2, 2, 1} as sequence))+( cast({4, 3, 3, 2} as multiset)))
======================
{1, 2, 2, 2, 3, 3, 3, 3, 3, 4}
```
```SELECT ((CAST ({3,3,3,2,2,1} AS SET))-(CAST ({4,3,3,2} AS MULTISET)));
```
``` (( cast({3, 3, 3, 2, 2, 1} as set))-( cast({4, 3, 3, 2} as multiset)))
======================
{1}
```
```SELECT ((CAST ({3,3,3,2,2,1} AS MULTISET))-(CAST ({4,3,3,2} AS MULTISET)));
```
``` (( cast({3, 3, 3, 2, 2, 1} as multiset))-( cast({4, 3, 3, 2} as multiset)))
======================
{1, 2, 3}
```
```SELECT ((CAST ({3,3,3,2,2,1} AS LIST))-(CAST ({4,3,3,2} AS MULTISET)));
```
``` (( cast({3, 3, 3, 2, 2, 1} as sequence))-( cast({4, 3, 3, 2} as multiset)))
======================
{1, 2, 3}
```
```SELECT ((CAST ({3,3,3,2,2,1} AS SET))*(CAST ({4,3,3,2} AS MULTISET)));
```
``` (( cast({3, 3, 3, 2, 2, 1} as set))*( cast({4, 3, 3, 2} as multiset)))
======================
{2, 3}
```
```SELECT ((CAST ({3,3,3,2,2,1} AS MULTISET))*(CAST ({4,3,3,2} AS MULTISET)));
```
``` (( cast({3, 3, 3, 2, 2, 1} as multiset))*( cast({4, 3, 3, 2} as multiset)))
======================
{2, 3, 3}
```
```SELECT ((CAST ({3,3,3,2,2,1} AS LIST))*(CAST ({4,3,3,2} AS MULTISET)));
```
``` (( cast({3, 3, 3, 2, 2, 1} as sequence))*( cast({4, 3, 3, 2} as multiset)))
======================
{2, 3, 3}
```

변수에 컬렉션 값 할당¶

컬렉션 값을 변수에 할당하기 위해서는 외부 질의가 하나의 행만을 반환해야 한다.

다음은 컬렉션 값을 변수에 할당하는 방법을 나타내는 예제이다. 다음과 같이 외부 질의는 하나의 행만을 반환해야 한다.

```CREATE TABLE people (
ssn VARCHAR(10),
name VARCHAR(255)
);

INSERT INTO people
VALUES ('1234', 'Ken'), ('5678', 'Dan'), ('9123', 'Jones');

SELECT SET(SELECT name
FROM people
WHERE ssn in {'1234', '5678'})
TO :name_group;
```