CARDINALITY

Description

The CARDINALITY function is used to calculate the number of elements in an array and the number of key-value pairs in a map.

Syntax

CARDINALITY(array)
CARDINALITY(map)

Parameter Description

• array: The input array, with elements of type T.
• map: The input map, consisting of key type K and value type V.

Return Type

• Returns an integer (int), representing the number of elements in the array or the number of key-value pairs in the map.

Usage Example

1. Calculate the number of elements in the array:

SELECT CARDINALITY(ARRAY(1, 2, 3, 4, 5)); -- Returns 5

2. Calculate the number of key-value pairs in the mapping:

SELECT CARDINALITY(MAP("a", 1, "b", 2, "c", 3)); -- Returns 3

3. Operate with actual data tables: Suppose there is a data table named students, with the following structure:

CREATE TABLE students (
  id INT,
  name VARCHAR,
  hobbies ARRAY<VARCHAR>
);

Insert a piece of data into the students table:

INSERT INTO students (id, name, hobbies) VALUES (1, 'Alice', ARRAY('reading', 'swimming', 'traveling'));

Using the CARDINALITY function to calculate the number of hobbies of the student:

SELECT CARDINALITY(hobbies) FROM students WHERE id = 1; -- return 3