Set Arithmetic Operators

SET, MULTISET, LIST

To compute union, difference or intersection of collections types (SET, MULTISET, and LIST (SEQUENCE)), you can use +, -, or * operators, respectively.

<value_expression>  <set_arithmetic_operator> <value_expression>

    <value_expression> ::=
        collection_value |
        NULL

    <set_arithmetic_operator> ::=
        + (union) |
        - (difference) |
        * (intersection)

The following table shows a result data type by the operator if collection type is an operand.

Result Data Type by Operand Type

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

The following are the examples which execute arithmetic operations with collection types.

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}

Assigning Collection Value to Variable

For a collection value to be assigned to a variable, the outer query must return a single row as a result.

The following example shows how to assign a collection value to a variable. The outer query must return only a single row as follows:

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;