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What is Cassandra Collections?

Cassandra collections are a good way for handling tasks. Multiple elements can be stored in collections. There are limitations in Cassandra collections.

  • Cassandra collection cannot store data more than 64KB.
  • Keep a collection small to prevent the overhead of querying collection because entire collection needs to be traversed.
  • If you store more than 64 KB data in the collection, only 64 KB will be able to query, it will result in loss of data.

There are three types of collections that Cassandra supports.

Cassandra Set

A Set stores group of elements that returns sorted elements when querying.

Syntax

Here is the syntax of the Set collection that store multiple email addresses for the teacher.

Create table University.Teacher
(
id int,
Name text,
Email set<text>,
Primary key(id)
);

Example

Here is the snapshot where table "Teacher" is created with "Email" column as a collection.

Cassandra Collections Tutorial - SET, LIST & MAP

Here is the snapshot where data is being inserted in the collection.

Cassandra Collections Tutorial - SET, LIST & MAP

insert into University.Teacher(id,Name,Email) values(l,'Guru99',{This email address is being protected from spambots. You need JavaScript enabled to view it.',This email address is being protected from spambots. You need JavaScript enabled to view it.'});

Cassandra List

When the order of elements matters, the list is used.

Here is the snapshot where column courses of list type id added in table "Teacher."

Cassandra Collections Tutorial - SET, LIST & MAP

Here is the snapshot where data is being inserted in column "coursenames".

Cassandra Collections Tutorial - SET, LIST & MAP

insert into University.Teacher(id,Name,Email) values(2,'Hamilton',{This email address is being protected from spambots. You need JavaScript enabled to view it.'},[Data Science']);

Here is the snapshot that shows the current database state after insertion.

Cassandra Collections Tutorial - SET, LIST & MAP

Cassandra Map

The map is a collection type that is used to store key value pairs. As its name implies that it maps one thing to another.

For example, if you want to save course name with its prerequisite course name, map collection can be used.

Here is the snapshot where map type is created for course name and its prerequisite course name.

Cassandra Collections Tutorial - SET, LIST & MAP

Here is the snapshot where data is being inserted in map collection type.

Cassandra Collections Tutorial - SET, LIST & MAP

insert into University.Course(id,prereq) values(1,'DataScience':'Database', 'Neural Network':'Artificial Intelligence'});

 

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