CQL Collections in Cassandra
Apache Cassandra is an open source, distributed, decentralized, elastically scalable, highly available, fault-tolerant, 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
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 data type 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 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 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 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 a 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 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 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 SELECT statement, you will get the following result:
cqlsh:xyz> SELECT * FROM data2;name | phone
--------+--------------------------------------
rahman | {9848022330, 9848022338, 9848022339}(1 rows)
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MAP
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, addressmap<timestamp, text>);
Inserting Data into a Map
While inserting data into the elements in a map, enter all the key : value pairs separated by 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 SELECT statement, you will get the following result:
cqlsh:xyz> select * from data3; name | address-------+-------------------------------------------
robin | {'home': 'hyderabad', 'office': 'mumbai'}(1 rows)
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