CQL Collections In Cassandra

Apache Cassandra is an open-source, distributed, decentralized, elastically scalable, highly available, fault-tolerant, a column-oriented database that bases its distribution design on Amazon’s Dynamo and its data model on Google’s Bigtable.

Cassandra Collections

CQL provides the facility of using Collection data types. Using these Collection types, you can store multiple values in a single variable.

List

The list is used in the cases where

the order of the elements is to be maintained, and

a value is to be stored multiple times.

You can get the values of a list of data types using the index of the elements in the list.

Creating a Table with List

Given below is an example to create a sample table with two columns, name and email. To store multiple emails, we are using a list.

cqlsh:tutorialspoint> CREATE TABLE data(name text PRIMARY KEY, email list);

Inserting Data into a List

While inserting data into the elements in a list, enter all the values separated by a comma within square braces [ ] as shown below.

cqlsh:tutorialspoint> INSERT INTO data(name, email) VALUES ('ramu',
['abc@gmail.com','cba@yahoo.com'])

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Updating a List

Given below is an example to update the list data type in a table called data. Here we are adding another email to the list.

cqlsh:tutorialspoint> UPDATE data
... SET email = email +['xyz@tutorialspoint.com']
... where name = 'ramu';

Verification

If you verify the table using a SELECT statement, you will get the following result:

cqlsh:tutorialspoint> SELECT * FROM data;
 name | email
------+--------------------------------------------------------------
 ramu | ['abc@gmail.com', 'cba@yahoo.com', 'xyz@tutorialspoint.com']
(1 rows)

SET

Set is a data type that is used to store a group of elements. The elements of a set will be returned in sorted order.

Creating a Table with Set

The following example creates a sample table with two columns, name and phone. For storing multiple phone numbers, we are using a set.

cqlsh:tutorialspoint> CREATE TABLE data2 (name text PRIMARY KEY, phone set<varint>);

Inserting Data into a Set

While inserting data into the elements in a set, enter all the values separated by a comma within curly braces { } as shown below.

cqlsh:tutorialspoint> INSERT INTO data2(name, phone)VALUES ('rahman',    {9848022338,9848022339});

Updating a Set

The following code shows how to update a set in a table named data2. Here we are adding another phone number to the set.

cqlsh:tutorialspoint> UPDATE data2
   ... SET phone = phone + {9848022330}
   ... where name = 'rahman';

Verification

If you verify the table using a SELECT statement, you will get the following result:

cqlsh:xyz> SELECT * FROM data2;
   name | phone
--------+--------------------------------------
 rahman | {9848022330, 9848022338, 9848022339}(1 rows)

Cassandra Interview Questions

MAP

A map is a data type that is used to store a key-value pair of elements.

Creating a Table with Map

The following example shows how to create a sample table with two columns, name and address. For storing multiple address values, we are using map.

cqlsh:xyz> CREATE TABLE data3 (name text PRIMARY KEY, address
map<timestamp, text>);

Inserting Data into a Map

While inserting data into the elements in a map, enter all the key: value pairs separated by a comma within curly braces { } as shown below.

cqlsh:xyz> INSERT INTO data3 (name, address)
   VALUES ('robin', {'home' : 'hyderabad' , 'office' : 'Delhi' } );

Updating a Set

The following code shows how to update the map data type in a table named data3. Here we are changing the value of the key office, that is, we are changing the office address of a person named robin.

cqlsh:xy> UPDATE data3
   ... SET address = address+{'office':'mumbai'}
   ... WHERE name = 'robin';

Verification

If you verify the table using a SELECT statement, you will get the following result:

cqlsh:xyz> select * from data3;  name | address
-------+-------------------------------------------
 robin | {'home': 'hyderabad', 'office': 'mumbai'}(1 rows)