step3-cassandra.md

Using Advanced Data Types in Apache Cassandra® ℹ️ For technical support, please contact us via email or LinkedIn.

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UUIDs

A universally unique identifier (UUID) is a 128-bit number that can be automatically generated and used to identify an entity or relationship in a Cassandra database. UUIDs provide an efficient way to assign unique identifiers and help to prevent accidental upserts or eliminate race conditions.

Cassandra Query Language supports the following two UUID data types:

• UUID is a Version 4 UUID that is randomly generated. To generate a value of type UUID, you can use function uuid().
• TIMEUUID is a Version 1 UUID that is generated based on a MAC address and a timestamp. To generate a value of type TIMEUUID, you can use function now(). When needed, the timestamp component of a TIMEUUID value can be extracted using functions unixTimestampOf() or dateOf(). Moreover, TIMEUUID values in clustering columns are automatically ordered based on their underlying timestamps and can also be retrieved based on the timestamps using functions minTimeuuid(timestamp) and maxTimeuuid(timestamp).

✅ As an example, let's create table users with partition key id of type UUID and insert two rows:

DROP TABLE IF EXISTS users;
CREATE TABLE users (
  id UUID,
  name TEXT,
  age INT,
  PRIMARY KEY ((id))
);

INSERT INTO users (id, name, age) 
VALUES (7902a572-e7dc-4428-b056-0571af415df3, 
       'Joe', 25);
INSERT INTO users (id, name, age) 
VALUES (uuid(), 'Jen', 27);

SELECT * FROM users;

✅ Next, create table movies with partition key id of type UUID and insert the following two rows:

id	title	year	duration
5069cc15-4300-4595-ae77-381c3af5dc5e	Alice in Wonderland	2010	108
uuid()	Alice in Wonderland	1951	75

Solution

DROP TABLE IF EXISTS movies;
CREATE TABLE movies (
  id UUID,
  title TEXT,
  year INT,
  duration INT,
  PRIMARY KEY ((id))
);

INSERT INTO movies (id, title, year, duration) 
VALUES (5069cc15-4300-4595-ae77-381c3af5dc5e, 
       'Alice in Wonderland', 2010, 108);
INSERT INTO movies (id, title, year, duration) 
VALUES (uuid(), 'Alice in Wonderland', 1951, 75);

SELECT * FROM movies;

✅ Finally, study this more advanced example, where TIMEUUID is used to both guarantee uniqueness and provide a timestamp for each row in table comments_by_user:

DROP TABLE IF EXISTS comments_by_user;
CREATE TABLE comments_by_user (
  user_id UUID,
  comment_id TIMEUUID,
  movie_id UUID,
  comment TEXT,
  PRIMARY KEY ((user_id), comment_id, movie_id)
);

INSERT INTO comments_by_user (user_id, comment_id, movie_id, comment) 
VALUES (7902a572-e7dc-4428-b056-0571af415df3, 
        63b00000-bfde-11d3-8080-808080808080, 
        5069cc15-4300-4595-ae77-381c3af5dc5e, 
        'First watched in 2000');
INSERT INTO comments_by_user (user_id, comment_id, movie_id, comment) 
VALUES (7902a572-e7dc-4428-b056-0571af415df3, 
        9ab0c000-f668-11de-8080-808080808080, 
        5069cc15-4300-4595-ae77-381c3af5dc5e, 
        'Watched again in 2010');
INSERT INTO comments_by_user (user_id, comment_id, movie_id, comment) 
VALUES (7902a572-e7dc-4428-b056-0571af415df3, 
        now(), 
        5069cc15-4300-4595-ae77-381c3af5dc5e, 
        'Watched again today');        

SELECT comment_id, dateOf(comment_id) AS date, comment
FROM comments_by_user
WHERE user_id = 7902a572-e7dc-4428-b056-0571af415df3;

SELECT comment_id, dateOf(comment_id) AS date, comment
FROM comments_by_user
WHERE user_id = 7902a572-e7dc-4428-b056-0571af415df3
  AND comment_id > maxTimeuuid('1999-01-01 00:00+0000')
  AND comment_id < minTimeuuid('2019-01-01 00:00+0000')
ORDER BY comment_id DESC;

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