Cassandra is a free and open-source NoSQL database management system designed to handle large amounts of data across many commodity servers, providing high availability with no single point of failure. Cassandra is an ideal choice for applications requiring continuous availability, high scalability, and high performance.
This tutorial will provide an introduction to Cassandra and its features. We will cover the basics of Cassandra, including its architecture, data model, query language, and storage engine. We will also discuss some of the most common tasks in Cassandra, such as creating a keyspace, creating a table, inserting data, and querying data.
We will also discuss some of the more advanced topics, such as replication, data consistency, and materialized views. Finally, we will discuss the tools available to help manage and monitor Cassandra clusters.
By the end of this tutorial, you will have a good understanding of Cassandra and its features. You will be able to create a Cassandra cluster and use it to store and query data. You will also be able to use the available tools to monitor and manage your Cassandra clusters.
Audience
This Cassandra tutorial is intended for anyone who wants to learn the basics of setting up and using Cassandra. It will cover topics such as installation, configuration, data modeling, and query language. After completing this tutorial, you will have the knowledge and skills necessary to start using Cassandra in your own projects.
Prerequisites
Before proceeding with this tutorial, we assume that you have basic knowledge on database concepts and familiarity with Cassandra NoSQL database.
Cassandra – Introduction
Cassandra is an open-source, distributed NoSQL database system. It is designed to provide scalability, high availability, and performance for today’s large-scale applications. Cassandra was initially developed by Facebook and later open-sourced in 2008. It is used by many organizations including Netflix, eBay, and Spotify. It is a highly reliable, fault-tolerant system with tunable consistency, allowing it to serve as the foundation of a wide variety of applications. Cassandra is written in Java and is available on many operating systems, including Windows, Linux, and Mac OS X.
NoSQLDatabase
NoSQL databases are non-relational databases that are designed to handle large sets of distributed data. Unlike traditional relational databases, NoSQL databases can store and process data without the need for extensive table structures. They are also designed to be flexible and scale easily, making them an ideal choice for applications that require rapid and high-volume data processing. NoSQL databases are often used for applications such as content management systems, web analytics, and social media platforms.
NoSQL vs. Relational Database
NoSQL and relational databases are two different types of databases. NoSQL databases are non-relational databases that are used to store, retrieve, and manage large amounts of unstructured data. They are ideal for applications that require scalability and high performance. NoSQL databases are schema-less and are built to provide flexibility and scalability to rapidly changing data.
Relational databases, on the other hand, are structured databases that use tables, columns, and rows to store information. They are used to store and manage structured data, and are ideal for applications that require complex data querying and transactions. They are also designed to maintain data integrity and consistency.
Besides Cassandra, we have the following NoSQL databases that are quite popular
1. MongoDB
2. HBase
3. CouchDB
4. Redis
5. Neo4J
6. Amazon DynamoDB
7. Accumulo
8. Riak
9. Terrastore
10. OrientDB
What is Apache Cassandra?
Apache Cassandra is an open-source, distributed, NoSQL database management system designed to handle large amounts of data across many commodity servers, providing high availability with no single point of failure. Cassandra offers robust support for clusters spanning multiple datacenters, with asynchronous masterless replication allowing low latency operations for all clients.
Features of Cassandra
1. High Availability: Cassandra is designed to be highly available and resilient, with no single point of failure. It provides a distributed and decentralized architecture that can automatically replicate data across multiple nodes.
2. Fault Tolerance: Cassandra is designed to be fault tolerant, meaning it can continue to operate even when a node fails. It is capable of automatically replicating data across multiple nodes, so that if one node fails, the data can still be accessed from another node.
3. Scalability: Cassandra is highly scalable and can easily be expanded to meet the growing needs of an organization. It supports linear scalability, meaning that it can scale up or down with minimal effort.
4. Data Model: Cassandra has a flexible data model that supports a wide variety of data types. It also supports both relational and non-relational databases, so it is suitable for a variety of applications
5. Security: Cassandra provides a number of security features such as authentication, authorization and encryption. It also supports role-based access control, which allows administrators to control who has access to certain data.
6. Performance: Cassandra is designed to be fast and efficient. It is capable of handling large amounts of data and queries with low latency. It also supports distributed caching, which allows for faster access to data.
History of Cassandra
The Cassandra database was first developed by Avinash Lakshman and Prashant Malik at Facebook in 2007. Initially, the project was called “Project Voldemort” and was used to power Facebook’s search infrastructure.
In 2008, the project was renamed to Cassandra and open-sourced. It was released under Apache License 2.0.
In 2010, DataStax was founded as a commercial implementation of Apache Cassandra.
In 2011, Cassandra became an Apache top-level project.
In 2013, Cassandra 2.0 was released and included features such as virtual nodes, improved performance, and a new API.
Over the years, Cassandra has been adopted by companies such as Apple, Netflix, eBay, and Twitter. It is now used in a wide variety of industries, ranging from banking and finance to social media and e-commerce.
Cassandra – Architecture
Cassandra is a distributed database management system designed to handle large amounts of data across multiple commodity servers, providing high availability with no single point of failure. It is a NoSQL database, which stores data in the form of columns and rows, and provides a high level of scalability, availability and performance.
At the core of Cassandra’s architecture is its ring-based data replication algorithm. Cassandra stores data on multiple nodes in a cluster, and replicates it across the cluster using a technique called replication factor. Replication factor is the number of times the data is replicated across the cluster. Each node in the cluster stores a replica of the data. This makes the data highly available, as the data can be retrieved from any node in the cluster.
Cassandra also provides a flexible data model, allowing for the definition of different data types and the ability to store data in a wide range of formats. This allows for the definition of data models based on user requirements.
Data Replication in Cassandra
Data replication in Cassandra is the process of copying and distributing data across multiple nodes in a cluster. This is done to improve scalability, reliability, and availability of data. Cassandra replicates data across multiple nodes using a replication factor. The replication factor is the number of replicas that each node will store. The higher the replication factor, the more copies of the data will be stored and the more reliable the data will be. Replication can be done manually or automated. With manual replication, the user is responsible for ensuring that all replicas are updated with the same data. With automated replication, the system will automatically replicate data across nodes.
In addition to its data model, Cassandra also provides a powerful query language called CQL (Cassandra Query Language). CQL allows users to query the Cassandra data model and to perform various operations on the data.
Finally, Cassandra provides a range of administrative and monitoring features, allowing administrators to manage, monitor and maintain the Cassandra cluster. These features include node management, security, backup and recovery, and performance monitoring.
Components of Cassandra
1. Cassandra Query Language (CQL): CQL is an SQL-like language used to access Cassandra’s data. It is used to create, update, delete, and query data in Cassandra.
2. Data Model: Cassandra’s data model is based on the concept of a column family. A column family is similar to a table in a relational database. A column family is composed of rows and each row contains a set of columns.
3. Gossip Protocol: The gossip protocol is used to maintain communication between nodes in a Cassandra cluster. It is used to keep track of all the nodes in the cluster and detect any changes in the nodes or the data they are storing.
4. SSTables: SSTables are files that store data in Cassandra. They are immutable, meaning that once data is written to an SSTable, it cannot be modified.
5. Commit Log: The commit log is a write-ahead log used to store all the changes made to the data stored in Cassandra. It is used to ensure that data is not lost in the event of a node failure.
6. Memtables: Memtables are in-memory structures used to store data that has been written to Cassandra. They are flushed to disk periodically to create SSTables.
7. Replication: Cassandra uses a replication strategy to replicate data across multiple nodes. This ensures that data is not lost if a node fails.
Cassandra Query Language
CQL is the Cassandra Query Language, a querying language for the Apache Cassandra database. CQL provides an SQL-like syntax for querying and managing Cassandra databases. It supports a wide range of operations including data definition, data manipulation, and data retrieval. CQL also provides a comprehensive set of data types for working with Cassandra data.
Write Operations
1. INSERT
INSERT INTO users (user_id, name, email) VALUES (1, ‘John’, ‘john@example.com’);
2. UPDATE
UPDATE users SET name = ‘John Doe’ WHERE user_id = 1;
3. DELETE
DELETE FROM users WHERE user_id = 1;
Read Operations
Read Operations in Cassandra Query Language
The following are read operations
1. SELECT: This is the most basic read operation in Cassandra. It is used to retrieve data from a particular table.
2. GET: This operation enables users to retrieve a single row from a table.
3. GET BY KEY: This is a specialized form of the GET operation, in which the row is retrieved using the primary key of the table.
4. RANGE SLICE: This operation enables users to retrieve a range of rows from a table. It can be used to retrieve data from a specified range of keys.
5. MULTIGET: This operation is used to retrieve multiple rows from a table.
6. MULTI RANGE SLICE: This operation is used to retrieve multiple rows from a table based on a specified range of keys.
7. SCAN: This operation is used to retrieve all the rows from a table. It can be used as an alternative to the SELECT query.
Cassandra – Data Model
Cassandra is a NoSQL database that uses a column-oriented data model. It is organized into tables, which are made up of columns, each of which can contain multiple data points. In Cassandra, data is stored in rows with columns that are organized into families. Each row is identified by a primary key and can contain any number of columns. The columns are grouped into column families, which provide a way to store related data points in a single table. Cassandra also supports secondary indexes, which allow for faster queries.
Cluster
A data model in Cassandra typically consists of a set of tables. Each table has a primary key which consists of one or more columns. Each table also contains a set of columns, which can contain a variety of data types.
In a Cassandra cluster, data is replicated across multiple nodes, so each node will have its own set of tables. The replication factor is set by the user, and determines how many replicas of the data will be stored. Data is distributed across the nodes in the cluster according to the configured replication factor.
When a query is made to a Cassandra cluster, the coordinator node will determine which nodes hold the required data and coordinate the query across them. The query will then be executed on each replica, and the coordinator will return the results to the user.
When data is inserted or updated in Cassandra, the coordinator node will ensure that the replicas are all updated with the same data. This ensures that the data remains consistent across the cluster.
Keyspace
A keyspace is a namespace that is used to store related data in Apache Cassandra. It is analogous to a database in a traditional relational database system. A keyspace is used to group a collection of tables that share a similar scope and purpose.
The basic attributes of a Keyspace in Cassandra are −
1. Name − It is the unique name of the Keyspace.
2. Replication Factor − It is the number of replicas of data across the cluster.
3. Strategy Class − It is the replication strategy used for data replication.
4. Replication Options − It is the settings for the replication strategy.
5. Durable Writes − It is the flag to enable or disable durability of data written to the Keyspace.
Column Family
A column family is a type of NoSQL database table that stores columns of related data together. It is a logical grouping of columns that are used to store data in a Cassandra database. It is similar to a table in a relational database and is used to store data in the form of key-value pairs.
| Column Family | Table of Relational Databases |
| ———— | —————————– |
| Columns have no predefined schema; columns can be added on the fly | Tables have a predefined schema; columns cannot be added on the fly |
| Complex data structures can be stored in a single row | Complex data structures must be broken into multiple rows and columns |
| Data is stored as key-value pairs or wide rows | Data is stored in a normalized form as rows and columns |
| Queries are faster and often more efficient | Queries are slower and less efficient |
| Scaling out is easy | Scaling out is difficult |
| Flexible data models | Rigid data models |
Column
A column in Cassandra is an individual component of a table row. It is the smallest unit of data in a database. It is analogous to a field in a relational database. A column consists of a name, a value, and a timestamp. The name is the unique identifier of the column. The value is the data stored in the column. The timestamp is the date and time when the column was last modified.
SuperColumn
A SuperColumn is a special type of column in the NoSQL database Cassandra. It is a collection of columns that are grouped together and stored as a single entity. A SuperColumn is similar to a regular column, except that it has multiple sub-columns that all belong to the same SuperColumn. This allows for better organization and allows related data to be stored together, instead of in separate columns. SuperColumns can also help to improve performance by reducing the amount of data that needs to be read from the database.
Data Models of Cassandra and RDBMS
Cassandra Data Model:
The Cassandra data model is based on the concept of a distributed key-value store. It uses a schema-optional storage model that allows users to store and access data without having to define a schema upfront. Cassandra stores data in the form of tables, with each row containing a key-value pair. Each row is identified by a unique key and can contain any number of columns, each containing a value.
RDBMS Data Model:
The RDBMS data model is based on the concept of a relational database. It uses a schema-based storage model that requires users to define a schema upfront. RDBMS stores data in the form of tables, with each table containing one or more rows. Each row contains columns that represent different attributes of the data stored in the row. Each column is identified by a unique name and contains a specific data type.
The following table lists down the points that differentiate the data model of Cassandra from that of an RDBMS.
| Data Model | Cassandra | RDBMS |
|—|—|—|
| Data Model | Column-oriented | Row-oriented |
| Distribution | Peer-to-peer | Centralized |
| Partition | Horizontal | Vertical |
| Data Schema | Dynamic | Fixed |
| Replication | Multiple copies across different nodes | Single copy in one node |
| Querying | CQL & Thrift | SQL |
| Transaction | No ACID transactions | Supports ACID transactions |
| Language | Java, C++, Python, Go | SQL |
| Sharding | Automatic | Manual |
Cassandra – Installation
The following steps should be followed to install Cassandra on an Ubuntu system:
1. First, update your local package index by running the command ‘sudo apt update’
2. Next, install the Cassandra package by running the command ‘sudo apt install cassandra’
3. Once the installation is complete, start the Cassandra service by running the command ‘sudo service cassandra start’
4. Verify that Cassandra is running by running the command ‘nodetool status’
5. If Cassandra is running, you should see something similar to the following output:
Datacenter: datacenter1
=======================
Status=Up/Down
|/ State=Normal/Leaving/Joining/Moving
— Address Load Tokens Owns (effective) Host ID Rack
UN 10.1.1.1 123.2 KB 256 100.0% 1a2b3c4d-5e6f-7a8b-9c0d-e1f2g3h4i5j rack1
6. Finally, to configure Cassandra, edit the configuration file ‘/etc/cassandra/cassandra.yaml’.
Congratulations, you have successfully installed Cassandra on your system!
Pre-Installation Setup of Cassandra
1. Install the Java Runtime Environment: Cassandra is written in Java and requires a Java Runtime Environment (JRE) to run. Install the latest version of JRE from the Oracle website.
2. Set the JAVA_HOME environment variable: After installing the Java Runtime Environment, it is important to set the JAVA_HOME environment variable. This is so that Cassandra knows where the Java installation is located.
3. Download the Cassandra binary: The Cassandra binary can be downloaded from the Apache Cassandra website. Make sure to download the latest version that is compatible with your operating system.
4. Configure the Cassandra configuration file: The Cassandra configuration file contains settings that are used to set up the Cassandra cluster. It is important to configure this file before starting the Cassandra service.
5. Set up the Cassandra data directories: Cassandra requires a data directory to store the data. This can be set up on the same server or a separate server.
6. Start the Cassandra service: After configuring the Cassandra configuration file and setting up the data directories, the Cassandra service can be started. This can be done by running the command “cassandra -f”.
7. Verify the installation: After starting the Cassandra service, it is important to verify the installation. This can be done by running the command “nodetool status”. This will show the status of the nodes in the Cassandra cluster.
SSH Setup and Key Generation
SSH, or Secure Shell, is a method of securely connecting to a networked computer system. It allows users to securely access and control a remote computer over an unsecured network, such as the Internet. SSH is widely used by system administrators to manage and secure their networks and servers.
Generating SSH keys is the first step to setting up an SSH connection. SSH keys are a pair of cryptographic keys that are used to authenticate a user to a remote host. The keys consist of a public key, which is used by the remote host to identify the user and verify the user’s identity, and a private key, which is used by the user to authenticate to the remote host.
To generate SSH keys, you will need to use an SSH key generator. Popular SSH key generators include PuTTYgen, ssh-keygen, and ssh-copy-id. Each of these tools has its own set of features, so you should research each of them to find the one that best meets your needs.
Once you have generated your SSH keys, you will need to add them to the remote host. This is usually done by copying the public key to the host’s authorized_keys file. Once the keys have been added, you will be able to establish an SSH connection to the remote host.
SSH is an essential tool for system administrators and anyone who needs to securely access and control remote systems. By generating SSH keys and adding them to the remote host, you can ensure that your network and systems are secure and that only authorized users can access them.
Installing Java
Java is the primary programming language used to write Cassandra applications. Cassandra requires a Java Runtime Environment (JRE) of version 8 or above. It is recommended to install the latest version of Java.
Download Cassandra
You can download Cassandra from the official Apache Cassandra website at https://cassandra.apache.org/download/. Choose the version you need and follow the instructions to install it on your system.
Configure Cassandra
1. Download the Cassandra software and install it on your system.
2. Start the Cassandra service with the command: “service cassandra start”.
3. Create a data directory for Cassandra, if you haven’t done so already.
4. Configure the Cassandra configuration file, cassandra.yaml, with the appropriate settings.
5. Create a Cassandra cluster using the command: “nodetool createcluster”.
6. Add nodes to the cluster by running the command: “nodetool addnode”.
7. Configure the Cassandra authentication and authorization settings.
8. Create a Cassandra keyspace and tables.
9. Setup a replication strategy for your Cassandra cluster.
10. Maintain the Cassandra cluster with the appropriate tools.
Create Directories
To create a directory in Cassandra, you can use the command mkdir. For example, to create a directory called “test”, you can type the following:
mkdir test
To make sure the directory has been successfully created, you can use the command ls to list the contents of the current directory. You should see the directory listed in the output.
Programming Environment
Programming with Cassandra typically involves developing applications using the Cassandra Query Language (CQL). CQL is a domain-specific language used to interact with the Cassandra database. It is similar to SQL and provides a familiar interface to developers who are already familiar with SQL. Additionally, developers can use Java, Python, or any other language that supports the Cassandra Driver.
To set up Cassandra programmatically, download the following jar files:
1. cassandra-all-3.11.4.jar
2. cassandra-driver-core-3.11.4.jar
3. cassandra-thrift-3.11.4.jar
4. cassandra-clientutil-3.11.4.jar
5. cassandra-mapping-3.11.4.jar
6. cassandra-driver-mapping-3.11.4.jar
7. cassandra-driver-extras-3.11.4.jar
8. cassandra-jdbc-3.11.4.jar
9. cassandra-logback-appender-3.11.4.jar
10. cassandra-utils-3.11.4.jar
11. jamm-0.3.2.jar
12. metrics-core-3.1.2.jar
13. guava-20.0.jar
14. netty-3.10.6.Final.jar
15. slf4j-api-1.7.25.jar
16. slf4j-log4j12-1.7.25.jar
17. log4j-1.2.17.jar
Eclipse Environment
Open Eclipse and create a new project called Cassandra _Examples.
1. Open Eclipse.
2. Click on File > New > Project.
3. Select Cassandra Examples from the list of available projects.
4. Enter a name for the project.
5. Click Finish to create the project.
6. In the project, create a new folder called Cassandra_Examples.
7. Place all Cassandra code and configuration files into this folder.
8. Configure Cassandra inside Eclipse.
9. You are now ready to start writing Cassandra code!
Maven Dependencies
Maven is a software project management and comprehension tool. It can manage dependencies and provide access to the correct version of a library for a project. Maven is commonly used for managing Java projects and can be used for managing dependencies of other programming languages as well. Maven dependencies are libraries, files, or plugins that are necessary for a project to build and run correctly. They are specified in the project’s pom.xml file, which is a Maven configuration file. Maven will automatically download the necessary dependencies when the project is built.
Given below is the pom.xml for building a Cassandra project using maven:
<project xmlns=”http://maven.apache.org/POM/4.0.0″ xmlns:xsi=”http://www.w3.org/2001/XMLSchema-instance”
xsi:schemaLocation=”http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd”>
<modelVersion>4.0.0</modelVersion>
<groupId>com.example.cassandra</groupId>
<artifactId>cassandra-example</artifactId>
<version>1.0</version>
<packaging>jar</packaging>
<name>cassandra-example</name>
<url>http://maven.apache.org</url>
<dependencies>
<dependency>
<groupId>org.apache.cassandra</groupId>
<artifactId>cassandra-all</artifactId>
<version>3.11.2</
Cassandra – Referenced Api
1. Apache Cassandra API: The official Apache Cassandra API provides access to the Apache Cassandra database and allows developers to build applications that can interact with the database.
2. Cassandra Java Driver: The Cassandra Java Driver is a low-level API that allows Java developers to interact with the Apache Cassandra database.
3. Cassandra Query Language (CQL): CQL is a high-level query language that provides an interface for developers to interact with the Cassandra database.
4. Cassandra Thrift API: The Cassandra Thrift API provides a low-level API that allows developers to access the Cassandra database using the Thrift network protocol.
5. Cassandra API for Python: The Cassandra API for Python provides a Python API for accessing the Cassandra database.
6. Cassandra API for Node.js: The Cassandra API for Node.js provides a Node.js API for accessing the Cassandra database.
Cluster
This class is the main entry point of the driver. It belongs to com.datastax.driver.core package.
The Driver class is the main entry point for using the DataStax Java Driver for Apache Cassandra. It is used to create Cluster instances, which can then be used to create Sessions. A Session is the main entry point for interacting with Cassandra and holds a connection pool to one or multiple Cassandra nodes.
The Driver class provides several static methods for creating a Cluster instance. The most common way to create a Cluster is by calling the connect() method, which takes a single argument, the contact point of the Cassandra cluster. The contact point can either be an IP address or a hostname.
Once a Cluster instance has been created, a Session can be created by calling the connect() method on the Cluster instance. The Session instance is used to execute statements and queries against Cassandra.
The Driver class also provides methods for configuring the driver, such as setting the connection pool size, the port to use, and the consistency level.
Cluster.Builder class
// (initially with no nodes).
Cluster.Builder cb = Cluster.builder();
// Configure the Cluster.Builder (for example, to set the port).
cb.addContactPoint(“127.0.0.1”);
cb.withPort(9042);
// Build the cluster
Cluster cluster = cb.build();
// Connect to the cluster and keyspace “mykeyspace”
Session session = cluster.connect(“mykeyspace”);
// Use the session to execute queries.
ResultSet rs = session.execute(“SELECT * FROM mytable;”);
// Process the results …
// …
// Close the session and cluster
session.close();
cluster.close();
Session
A session in Cassandra cluster is a client-side object that represents a connection to a Cassandra cluster. It can be used to execute queries, update data and read data from the cluster. The session is responsible for maintaining a connection to the cluster, managing the state of the cluster, and providing a way to execute queries. Sessions also provide methods for setting up authentication and authorization of access to the cluster. Sessions are generally created using the Cassandra Cluster class.
Cassandra – Cqlsh
Cqlsh is a command line shell for interacting with Cassandra databases. It is used to execute CQL (Cassandra Query Language) commands against a Cassandra cluster, allowing users to create and manage keyspaces and tables, to run queries, and to perform various administrative tasks. It also allows users to connect to remote servers, perform backups, and monitor the status of the Cassandra cluster. Cqlsh is available for Windows, Linux, and Mac OS X.
Starting cqlsh
To start cqlsh, open a terminal window and enter the following command:
Cqlsh
Cqlsh Commands
Cqlsh is a command line shell for interacting with Cassandra databases. It provides an interactive way to communicate with Cassandra through the Cassandra Query Language (CQL).
The main options available in cqlsh are:
1. Connect – This enables you to connect to a Cassandra cluster. You can specify the hostname, port, and username and password to connect to the cluster.
2. Execute – This command allows you to execute any CQL command.
3. Help – This command displays help information about the available CQL commands, as well as the CQL shell itself.
4. Exit – This command exits the CQL shell.
5. Describe – This command displays information about the Cassandra keyspace, table and columns
6. Copy – This command allows you to copy data from a file into a Cassandra table
7. Show – This command displays information about the Cassandra schema, such as keyspaces, tables, and columns.
8. Source – This command executes CQL commands from a file
9. Consistency – This command sets the consistency level for CQL queries.
10. Trace – This command enables you to trace a C
Documented Shell Commands
The following are some examples of documented shell commands:
1. cd – change directory
2. ls – list directory contents
3. mv – move or rename files
4. cp – copy files
5. mkdir – make directories
6. rm – remove files and directories
7. grep – search for patterns in files
8. chmod – change permissions on files
9. find – search for files by name
10. man – access the online manual
CQL Data Definition Commands
1. CREATE KEYSPACE: Creates a new keyspace.
2. DROP KEYSPACE: Drops an existing keyspace.
3. CREATE TABLE: Creates a new table.
4. ALTER TABLE: Alters an existing table.
5. DROP TABLE: Drops an existing table.
6. CREATE INDEX: Creates a new index.
7. DROP INDEX: Drops an existing index.
8. TRUNCATE: Deletes all data in a table.
9. CREATE TYPE: Creates a new user-defined type.
10. ALTER TYPE: Alters an existing user-defined type.
11. DROP TYPE: Drops an existing user-defined type.
CQL Data Manipulation Command
1. SELECT: Used to retrieve rows from a table.
2. INSERT: Used to insert rows into a table.
3. UPDATE: Used to modify existing rows in a table.
4. DELETE: Used to delete existing rows from a table.
5. CREATE: Used to create a new table.
6. ALTER: Used to modify an existing table.
7. TRUNCATE: Used to delete all the rows from a table.
8. DROP: Used to delete an entire table.
CQL Clauses
1. SELECT: Used to retrieve data from a table.
2. WHERE: Used to specify criteria for selecting data from a table.
3. GROUP BY: Used to group rows based on a given set of criteria.
4. ORDER BY: Used to sort rows in a table according to a given set of criteria.
5. LIMIT: Used to limit the number of rows returned in a query.
6. CREATE TABLE: Used to create a new table in a database.
7. ALTER TABLE: Used to modify the structure of an existing table.
8. DROP TABLE: Used to delete an entire table from a database.
Cassandra – Shell Command
1. DESCRIBE: This command will provide information about the keyspace and its tables.
2. SHOW KEYSPACES: This command will show all the keyspaces in the Cassandra cluster.
3. CREATE KEYSPACE: This command will create a new keyspace.
4. USE: This command will switch the active keyspace.
5. CREATE TABLE: This command will create a new table in the current keyspace.
6. DROP KEYSPACE: This command will delete an existing keyspace.
7. ALTER TABLE: This command will modify an existing table
8. INSERT INTO: This command will add data to a table.
9. SELECT: This command will retrieve data from a table.
10. UPDATE: This command will update data in a table.
11. DELETE: This command will delete data from a table.
12. Describe Type: The type command is a Windows command used to display the contents of a text file. It is used to display the contents of a file on the screen or to print the contents of a file to a printer. It can also be used to compare two files and output the differences between them.
Cassandra – Create Keyspace
Creating a Keyspace using Cqlsh
To create a Keyspace using Cqlsh, first open the Cqlsh shell and then enter the following command:
CREATE KEYSPACE <keyspace_name> WITH REPLICATION = { ‘class’ : ‘SimpleStrategy’, ‘replication_factor’ : <number_of_replicas> };
Replace <keyspace_name> with the desired name of the Keyspace and <number_of_replicas> with the desired number of replicas.
Replication
Replication replica placement strategy is the process of deciding where to place copies of data in order to ensure data availability and reduce latency. This typically involves finding a balance between the total cost of hosting the data and the performance requirements of the application. A common approach is to use a combination of primary and secondary replicas, with the primary replica being the main source of data, and the secondary replicas providing additional redundancy. The placement of replicas should take into account factors such as network latency, disk throughput, and disk capacity. It is also important to consider the cost of replacing a failed replica, and the impact of the replica placement strategy on data consistency.
example of creating a KeySpace
// CREATE KEYSPACE mykeyspace WITH REPLICATION = { ‘class’ : ‘NetworkTopologyStrategy’, ‘datacenter1’ : 3 };
Verification
Verifying replication in Cassandra is a relatively simple process. The most reliable way is to use the nodetool utility, which can be used to check the status of replication across all nodes in a cluster.
To view the replication factor of each node, use the following command:
nodetool status
This will show the replication factor for each node, as well as the number of replicas each node is responsible for.
To verify that data is being replicated correctly, you can use the nodetool getendpoints command. This will show the replicas of a given key and the data centers they are located in.
If the data centers are different, this confirms that data is being replicated across data centers. You can also use the nodetool getreplicas command to get the replicas of a given key and their respective IP addresses. This will allow you to verify that the data is being replicated to the correct nodes.
Durable_writes
Durable writes is a feature of a database that ensures that once data has been written to the database, it will remain persistent even if the database experiences a power failure or other abrupt interruption. Durable writes are a critical feature of a database because it ensures the integrity and accuracy of the data stored in the database. Without this feature, a power failure could cause data to be lost or corrupted, leading to incorrect or missing information.
Verification
To verify that Durable_writes is enabled, you can use the nodetool command to check the Cassandra cluster configuration. The command is as follows:
nodetool describecluster
This will display the cluster configuration and you can verify whether the durable_writes option is set to true.
Creating a Keyspace using Java API
1. Add the Java Cassandra Driver to your project.
2. Establish a connection to your Cassandra cluster.
3. Create a Session object and use it to create a Keyspace
4. Define the Keyspace properties, such as replication strategy and replication factors
5. Execute the Keyspace creation query using the Session object’s execute() method.
6. Close the Session connection.
//Create Cluster object
Cluster cluster = Cluster.builder().addContactPoint(“127.0.0.1”).build();
//Create Session object
Session session = cluster.connect();
//Create Keyspace using SimpleStrategy
String query = “CREATE KEYSPACE mykeyspace WITH replication “
+ “= {‘class’:’SimpleStrategy’, ‘replication_factor’:1};”;
session.execute(query);
Cassandra – Alter Keyspace
To alter an existing keyspace, the ALTER KEYSPACE command is used.
Syntax: ALTER KEYSPACE <keyspace_name> WITH <option> = <value> [AND <option> = <value> …]
For example, to alter a keyspace named “mykeyspace” to have the replication factor set to 3, the following command can be used:
ALTER KEYSPACE mykeyspace WITH replication = {‘class’: ‘SimpleStrategy’, ‘replication_factor’ : 3};
Given below is an example of altering a KeySpace
CREATE KEYSPACE example WITH REPLICATION = { ‘class’ : ‘SimpleStrategy’, ‘replication_factor’ : 3 };
ALTER KEYSPACE example WITH REPLICATION = { ‘class’ : ‘NetworkTopologyStrategy’, ‘datacenter1’ : 2, ‘datacenter2’ : 2 };
Replication
Replication in an Alter Keyspace statement is used to configure replication for an existing keyspace. It is used to set up the replication factor, the data center replication strategies, and the replication options. The replication factor determines the number of replicas of data that will be stored across the cluster and the data center replication strategies determine which nodes will have replicas of the data. The replication options define the consistency levels and other settings.
Durable_writes
Durable writes is a feature of Cassandra which allows writes to be committed to disk after they have been written to memory. This ensures that data is not lost in the case of a power failure or other unexpected event. With durable writes, Cassandra is able to guarantee that committed writes will remain in the database, even if the server is offline or experiences a crash.
Altering Durable_writes
In order to alter the value of durable_writes, a user must have the privileges to do so. Depending on the database system being used, the command to alter the value of durable_writes will vary. For example, to alter the value of durable_writes in PostgreSQL, a user would use the ALTER SYSTEM command. The syntax would look like this: ALTER SYSTEM SET durable_writes = ‘on’ or ALTER SYSTEM SET durable_writes = ‘off’;.
Altering a Keyspace using Java API
1. Create a Java application and include the Cassandra Java driver.
2. Connect to the Cassandra cluster using the Java driver.
3. Use the Session.execute() method to execute ALTER KEYSPACE query.
4. Use the Session.executeAsync() method to execute ALTER KEYSPACE queries asynchronously.
5. Modify the Keyspace as desired.
6. Use the Session.execute() or Session.executeAsync() method to execute the ALTER KEYSPACE query with the modified parameters.
7. Disconnect from the Cassandra cluster.
import com.datastax.driver.core.Cluster;
import com.datastax.driver.core.Session;
public class AlterKeyspace {
public static void main(String args[]){
//Query
String query = “ALTER KEYSPACE tutorialspoint WITH REPLICATION = { ‘class’ : ‘SimpleStrategy’, ‘replication_factor’ : 3 };”;
//Creating Cluster object
Cluster cluster = Cluster.builder().addContactPoint(“127.0.0.1”).build();
//Creating Session object
Session session = cluster.connect();
//Executing the query
session.execute(query);
System.out.println(“Keyspace altered”);
}
}
Cassandra – Drop Keyspace
Dropping a Keyspace
To drop a keyspace, use the DROP KEYSPACE statement.
Syntax:
DROP KEYSPACE <keyspace_name>;
Verification
In Cassandra, you can drop a keyspace using the DROP KEYSPACE command. The syntax for this command is as follows:
DROP KEYSPACE <keyspace_name> [IF EXISTS];
This command will delete the specified keyspace and all of its data. If the keyspace does not exist, Cassandra will return an error. Therefore, it is recommended to use the IF EXISTS clause to avoid such errors.
Dropping a Keyspace using Java API
Steps in Dropping a Keyspace using Java API
1. Create an instance of Cluster object.
2. Connect to the Cassandra server using the connect() method.
3. Create an instance of the Keyspace object.
4. Use the execute() method to drop the Keyspace.
5. Close the connection.
//Create a cluster and session from the Cassandra cluster
Cluster cluster = Cluster.builder().addContactPoints(“127.0.0.1”).build();
Session session = cluster.connect();
//Drop the keyspace
String query = “DROP KEYSPACE <keyspace_name>;”;
session.execute(query);
//Close the session and cluster
session.close();
cluster.close();
Cassandra – Create Table
Creating a Table in Cassandra
CREATE TABLE users (
user_id UUID PRIMARY KEY,
first_name text,
last_name text,
email text
);
Defining a Column
In Cassandra, a column is a specific data element that is stored in a row of a table. A column consists of a name, a value, and a timestamp. The name and value together form a pair, also known as a cell. Each column in a row is identified by its name and can have one or more values associated with it. The timestamp is used to keep track of when the column was last modified.
Primary Key
A primary key is a unique identifier for a row in a database table. It ensures that each row in the table is uniquely identified by the primary key, and it cannot be changed or duplicated. It is typically a single field or a combination of fields that uniquely identify a record in a database table.
Example
A primary key is a unique identifier, often a single field or combination of fields, used to uniquely identify a record in a database table.
For example, a customer table in a database may have a customer ID field as its primary key. This field would contain a unique value for each customer, such as a customer number or social security number. No two customers would have the same customer ID, ensuring that each customer can be identified uniquely in the database.
Creating a Table using Java API
1. Create a DatabaseConnection object to connect to the database.
2. Execute a query to create the table using the createTable() method of the DatabaseConnection object.
3. Set the columns of the table using the setColumns() method of the DatabaseConnection object.
4. Set the primary key for the table using the setPrimaryKey() method of the DatabaseConnection object.
5. Execute the query to create the table using the executeQuery() method of the DatabaseConnection object.
6. Close the DatabaseConnection object using the closeConnection() method of the DatabaseConnection object.
//Create a table
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.Statement;
public class TableCreation {
public static void main(String[] args) {
Connection con = null;
Statement stmt = null;
String tableName = “STUDENT”;
String createTableSQL = “CREATE TABLE ” + tableName + “(” +
“ID INT NOT NULL, ” +
“NAME VARCHAR(20) NOT NULL, ” +
“AGE INT NOT NULL, ” +
“PRIMARY KEY (ID) ” +
“)”;
try {
//Registering the Driver
Class.forName(“oracle.jdbc.driver.OracleDriver”);
//Creating the connection
con = DriverManager.getConnection(
“jdbc:oracle:thin:@localhost:1521:orcl”, “root”, “password”);
//Creating the Statement
stmt = con.createStatement();
//Executing the query
stmt.executeUpdate(createTableSQL);
System.out.println(“Table ” + tableName + ” is created!”);
} catch (Exception e) {
System.out.println(e);
} finally {
//Closing the connection
try {
con.close();
} catch (Exception e) {
System.out.println(e);
}
}
}
}
Cassandra – Alter Table
To alter an existing table in Cassandra, the ALTER TABLE statement can be used.
Syntax:
ALTER TABLE <table_name>
ADD <column_name> <column_type> [WITH OPTIONS];
Example:
ALTER TABLE users
ADD age INT;
Altering a Table
ALTER TABLE table_name
ALTER column_name TYPE data_type;
Example:
ALTER TABLE customer
ALTER email TYPE text;
Adding a Column
ALTER TABLE <tableName> ADD <columnName> <dataType>;
Dropping a Column
DROP COLUMN <column_name> FROM <table_name>;
Altering a Table using Java API
1. Create a Connection to the Database: The first step is to create a connection to the database using a JDBC driver. This will allow you to access the database and make changes to it.
2. Use DatabaseMetaData to Get Table Information: Once you have a connection to the database, you can use the DatabaseMetaData interface to get information about the tables in the database. This will allow you to see which tables you need to alter.
3. Create a Statement Object: You will need to create a Statement object in order to make changes to the table. This object will allow you to execute SQL commands against the database.
4. Execute an ALTER TABLE Command: Once you have a Statement object, you can execute an ALTER TABLE command to make changes to the table. This will allow you to add, remove, or modify columns, as well as other table properties
5. Commit the Changes: After you have made changes to the table, you will need to commit the changes in order for them to take effect. This can be done with the commit() method of the Connection object.
6. Close the Connection: Finally, you will need to close the connection to the database. This will ensure that any changes you have made are saved and that the database remains secure.
import java.sql.Connection;
import java.sql.Statement;
public class AlterTableExample {
public static void main(String[] args) {
try {
//Creating a connection
Connection con = Database.getConnection();
Statement stmt = con.createStatement();
//Adding a new column
String query1 = “ALTER TABLE student ADD COLUMN address varchar(50)”;
stmt.executeUpdate(query1);
System.out.println(“Column added successfully”);
//Adding a new column
String query2 = “ALTER TABLE student MODIFY COLUMN name varchar(40)”;
stmt.executeUpdate(query2);
System.out.println(“Column modified successfully”);
//Modifying the data type of a column
String query3 = “ALTER TABLE student MODIFY COLUMN age int(10)”;
stmt.executeUpdate(query3);
System.out.println(“Data type modified successfully”);
//Dropping a column
String query4 = “ALTER TABLE student DROP COLUMN address”;
stmt.executeUpdate(query4);
System.out.println(“Column deleted successfully”);
//Closing the connection
con.close();
} catch (Exception e) {
System.out.println(e);
}
}
}
Deleting a Column
Given below is the complete program to delete a column from an existing table.
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.Statement;
public class DeleteColumn {
public static void main(String[] args) {
try {
//Registering the Driver
Class.forName(“com.mysql.cj.jdbc.Driver”);
//Getting the connection
Connection con = DriverManager.getConnection(“jdbc:mysql://localhost:3306/testdb”, “username”, “password”);
//Creating a statement
Statement stmt = con.createStatement();
//Query to delete the column
String query = “ALTER TABLE employees DROP COLUMN salary”;
//Executing the query
stmt.executeUpdate(query);
System.out.println(“Column deleted successfully”);
} catch (Exception e) {
e.printStackTrace();
}
}
}
Cassandra – Drop Table
To drop a table in Cassandra, you need to use the DROP TABLE command. This command will delete the entire table, including all of its data, from the Cassandra database.
1. Create an instance of the DatabaseMetaData class from the Connection object.
2. Execute the getTables() method of the DatabaseMetaData object to retrieve the table names in the database.
3. Iterate through the list of table names and identify the table to be deleted.
4. Create an instance of the Statement class from the Connection object.
5. Execute the executeUpdate() method of the Statement object to execute the DROP TABLE SQL command.
6. Close the Connection and Statement objects.
You must specify the keyspace and the table name when executing this command. For example:
DROP TABLE keyspace_name.table_name;Syntax:
DROP TABLE <table_name>;
Given below is the complete program to drop a table in Cassandra using Java API.
import com.datastax.driver.core.Cluster;
import com.datastax.driver.core.Session;
public class CassandraDropTable {
public static void main(String args[]) {
//Query
String query = “DROP TABLE emp;” ;
//Creating Cluster object
Cluster cluster = Cluster.builder().addContactPoint(“127.0.0.1”).build();
//Creating Session object
Session session = cluster.connect(“tp”);
//Executing the query
session.execute(query);
//using the KeySpace
System.out.println(“Table dropped”);
}
}
Cassandra – Truncate Table
To truncate a table in Cassandra, the following command syntax should be used:
TRUNCATE <table_name>;
Verification
In truncate table, the data is not physically removed from the table but the data is logically removed from the table. A verification process is not necessary in truncate table as all the data associated with the table is removed.
Truncating a Table using Java API
1. Establish a connection to the database using the JDBC driver.
2. Create a Statement object by calling the createStatement() method of the Connection object.
3. Create a TruncateTableQuery and assign it to a String variable.
4. Execute the query by calling the executeUpdate() method of the Statement object and passing the TruncateTableQuery as an argument.
5. Close the connection to the database by calling the close() method of the Connection object.
Truncating a Table using Java API
PreparedStatement pstmt = conn.prepareStatement(“TRUNCATE TABLE tableName”);
pstmt.executeUpdate();
Cassandra – Create Index
CREATE INDEX ON table (column);
Creating an Index using Cqlsh
1. Log into Cqlsh:
cqlsh
2. Create keyspace and switch to it:
CREATE KEYSPACE mykeyspace WITH REPLICATION = { ‘class’ : ‘SimpleStrategy’, ‘replication_factor’ : 3 };
USE mykeyspace;
3. Create table:
CREATE TABLE products (
product_id int,
product_name text,
product_brand text,
PRIMARY KEY (product_id)
);
4. Insert data:
INSERT INTO products (product_id, product_name, product_brand) VALUES (1, ‘shoes’, ‘Nike’);
INSERT INTO products (product_id, product_name, product_brand) VALUES (2, ‘socks’, ‘Adidas’);
INSERT INTO products (product_id, product_name, product_brand) VALUES (3, ‘hat’, ‘Puma’);
5. Create index:
CREATE INDEX product_brand_index ON products (product_brand);
Creating an Index using Java API
1. Establish a Java Database Connection: Establish a connection to a database using the Java Database Connectivity (JDBC) API. This will allow you to access and manipulate the data in the database.
2. Create a Table: Create a table in the database which will store the index information. This table will need to store the name of the indexed column, the type of the indexed column, and the index name.
3. Create an Index: Use the Java API to create an index in the table. This will specify which column is indexed, the type of the index, and the name of the index.
4. Insert Data into the Table: Insert the data into the table using the Java API. Be sure to include the indexed column in the data that is inserted.
5. Drop the Index: Use the Java API to drop the index from the table. This will delete the index from the table.
6. Close the Connection: Close the connection to the database. This will ensure that all changes have been saved and that the index has been removed.
//Create an Index
IndicesAdminClient indicesAdminClient = client.admin().indices();
//Create a request
CreateIndexRequest request = new CreateIndexRequest(“index_name”);
//Create a mapping
request.mapping(“_doc”,
“name”, “type=text”,
“age”, “type=integer”
);
//Create the index
CreateIndexResponse response = indicesAdminClient.create(request).actionGet();
//Check if the index was created successfully
boolean acknowledged = response.isAcknowledged();
Cassandra – Drop Index
To drop an index in Cassandra, you need to use the DROP INDEX command.
For example, if you have a table named users with a column name “email”, then you can drop the index for that column using the following command:
DROP INDEX users_email_idx;
Dropping an Index
DROP INDEX index_name ON table_name;
Dropping an Index using Java API
1. Create a Java Database Connection: Establish a connection to the database using the JDBC driver. This will require the appropriate database URL, username, and password.
2. Create a Statement Object: Create a java.sql.Statement object for the connection.
3. Execute the DROP INDEX Statement: Use the statement object created in step 2 to execute the DROP INDEX statement. This statement should include the name of the index being dropped.
4. Close the Database Connection: Finally, close the database connection.
//Dropping an index using the Java API
//Create the Java Client object
RestHighLevelClient client = new RestHighLevelClient(
RestClient.builder(
new HttpHost(“localhost”, 9200, “http”)
)
);
//Create the IndexRequest object
DeleteIndexRequest request = new DeleteIndexRequest(“my_index”);
//Send the request to the Elasticsearch server
AcknowledgedResponse response = client.indices().delete(request, RequestOptions.DEFAULT);
//Check the response
if(response.isAcknowledged()) {
System.out.println(“Index deleted successfully.”);
}
Cassandra – Batch Statements
Cassandra supports batch statements which allow multiple operations to be performed in a single transaction. This allows for faster processing of data queries and updates. A batch statement can contain any combination of data manipulation language (DML) statements and query language (QL) statements. The data manipulation language statements include insert, update, delete, and truncate. The query language statements include select, show, and describe. The batch statement is executed as a single atomic unit and will fail if any of the statements fail. This ensures that data integrity is maintained.
Using Batch Statements
Batch statements are used to execute multiple SQL statements as a single unit. This allows for multiple statements to be executed at the same time, which can be more efficient than executing multiple individual statements. Batch statements are typically used when multiple statements need to be executed in a specific order or if multiple statements need to be executed in a single transaction. Batch statements can also be used to execute multiple statements that would be difficult or impossible to execute in a single statement.
Batch Statements using Java API
1. Create a BatchStatement object.
2. Use the add() method to add your individual statements to the BatchStatement object.
3. Execute the BatchStatement object using the execute() method.
4. Process the results of the BatchStatement as desired.
//Batch Statement 1
String query1 = “INSERT INTO Customers (CustomerName, City, Country) VALUES (‘Cardinal’, ‘Stavanger’, ‘Norway’)”;
String query2 = “INSERT INTO Customers (CustomerName, City, Country) VALUES (‘Alfreds Futterkiste’, ‘Berlin’, ‘Germany’)”;
String query3 = “INSERT INTO Customers (CustomerName, City, Country) VALUES (‘Ernst Handel’, ‘Graz’, ‘Austria’)”;
Statement stmt = conn.createStatement();
stmt.addBatch(query1);
stmt.addBatch(query2);
stmt.addBatch(query3);
stmt.executeBatch();
//Batch Statement 2
String query4 = “UPDATE Customers SET City = ‘Stuttgart’ WHERE CustomerName = ‘Alfreds Futterkiste'”;
String query5 = “UPDATE Customers SET Country = ‘Germany’ WHERE CustomerName = ‘Ernst Handel'”;
Statement stmt = conn.createStatement();
stmt.addBatch(query4);
stmt.addBatch(query5);
stmt.executeBatch();
Cassandra – Create Data
CREATE KEYSPACE music_store WITH replication = {‘class’: ‘SimpleStrategy’, ‘replication_factor’: 2};
CREATE TABLE music_store.albums (
album_id int,
album_name text,
artist_name text,
release_date timestamp,
PRIMARY KEY (album_id)
);
INSERT INTO music_store.albums (album_id, album_name, artist_name, release_date)
VALUES (1, ‘Thriller’, ‘Michael Jackson’, ‘1982-11-30’);
INSERT INTO music_store.albums (album_id, album_name, artist_name, release_date)
VALUES (2, ‘The Dark Side of the Moon’, ‘Pink Floyd’, ‘1973-03-01’);
Creating Data in a Table
Table 1
| Item | Price |
|——–|——-|
| Apple | $1.00 |
| Banana | $2.00 |
| Orange | $3.00 |
Creating Data using Java API
1. Define the data structure. Decide what type of data you need to store and use, such as strings, ints, doubles, and objects.
2. Create a class that will hold the data. This class should have fields that correspond to the data structure you defined.
3. Create a constructor for the class that initializes the fields.
4. Create getter and setter methods for each field in the class.
5. Create a method that will populate the data structure with data. This could be a method that takes in a list of objects or a method that takes in a database connection and reads in the data from the database.
6. Once the data is populated, you can use the getter and setter methods to access and modify the data in the data structure.
7. Finally, create a method that will write the data back to the database or to a file.
//Creating a list of strings
List<String> stringList = new ArrayList<>();
stringList.add(“Hello”);
stringList.add(“World”);
//Creating a map of string and integers
Map<String, Integer> stringIntegerMap = new HashMap<>();
stringIntegerMap.put(“One”, 1);
stringIntegerMap.put(“Two”, 2);
//Creating an array of integers
int [] intArr = {1,2,3,4};
Cassandra – Update Data
To update data in Cassandra, you can use the UPDATE command. The syntax is as follows:
UPDATE <keyspace_name>.<table_name> SET <column_name> = <value> WHERE <column_name> = <value>;
For example, if you want to update the name of a customer in the customers table of the my_keyspace keyspace, you can use the following command:
UPDATE my_keyspace.customers SET name=’John Doe’ WHERE id=123;
Updating data in a table can be done using an UPDATE statement. The syntax for this statement is as follows:
UPDATE table_name
SET column1 = value1, column2 = value2, …
WHERE condition;
This statement will update the values of the specified columns in the table where the condition is met. For example, if we wanted to update the quantity of an item in the table, we could use the following statement:
UPDATE items
SET quantity = 500
WHERE item_name = ‘Pen’;
Cassandra – Read Data
The Cassandra read data operation is accomplished using the SELECT command. This command is used to query data stored in tables. The results of the query can be filtered, grouped, and ordered based on the requirements of the user.
The SELECT command can be used to retrieve specific columns from a table, or all the columns, using the asterisk (*) symbol. The WHERE Clause is used to filter the results of the query. The ORDER BY Clause is used to sort the results in ascending or descending order. The GROUP BY Clause is used to group the results of the query. The LIMIT Clause is used to limit the number of results returned.
Reading Data using Select Clause
SELECT * FROM table_name;
This query will retrieve all data from the specified table.
The SELECT command can be used in conjunction with other commands such as UPDATE, INSERT, and DELETE to manipulate data in the database.
Reading Required Columns
The required columns that are needed to track project progress are:
1. Project Name
2. Start Date
3. End Date
4. Milestones
5. Tasks
6. Status
7. Resources
8. Budget
9. Issues/Risks
Where Clause
The WHERE Clause is used to filter records. It is used in SELECT, UPDATE and DELETE statements to filter the results of the query. The WHERE clause can use comparison operators such as =, <, >, <=, >=, and LIKE. It can also use logical operators such as AND, OR and NOT. For example:
SELECT * FROM table_name
WHERE column_name = ‘some_value’
AND column_name2 > 10
OR column_name3 NOT LIKE ‘%string%’
Reading Data using Java API
Java provides a number of APIs to read data from different sources. The most common API used for reading data is the Java Database Connectivity (JDBC) API. This API is used to access databases and query them for data. Other APIs used for reading data are the Java Native Interface (JNI) API, Java NIO API, Java File API, and the Apache POI API. Each of these APIs have their own advantages and disadvantages when it comes to reading data.
1. Establish a connection to the database: Use the JDBC driver to connect to the database. This is typically done by obtaining a Connection object from the DriverManager class.
2. Create a statement: Once the connection is established, create a statement object. This object will be used to execute all SQL queries.
3. Execute the query: Execute the query by using the statement object.
4. Process the results: Use the ResultSet object to access the results of the query. Process the data as required.
5. Close the connection: Close the connection to the database. This is done by calling the close() method of the Connection object.
Cassandra – Delete Data
To delete data from Cassandra, you can use the DELETE command.
Here is an example of how to use the DELETE command:
DELETE FROM users WHERE user_id = ‘12345’;
Deleting Datafrom a Table
To delete data from a table, use the DELETE statement in SQL. The syntax for the DELETE statement is:
DELETE FROM [table_name] WHERE [condition];
For example, to delete all rows from a table named ‘users’ where the age is greater than 50, you can use the following statement:
DELETE FROM users WHERE age > 50;
Deleting an Entire Row
To delete an entire row in Excel, select the row and right-click on it. Then, select ‘Delete’ from the menu that appears. This will delete the entire row.
Deleting Data using Java API
1. Establish a database connection using the Java Database Connectivity (JDBC) API. This can be accomplished by using the DriverManager class to connect to the database.
2. Create a Statement object to execute the SQL commands.
3. Write an SQL query to delete the data from the database table.
4. Execute the statement using the executeUpdate() method.
5. Close the connection to the database.
The Java API can be used to delete data from databases. The java.sql.Statement class allows for the execution of SQL DELETE statements.
Example:
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.Statement;
public class DeleteDataFromTable {
public static void main (String[] args) {
Connection con = null;
Statement stmt = null;
try {
Class.forName(“com.mysql.jdbc.Driver”);
con = DriverManager.getConnection(“jdbc:mysql://localhost:3306/databaseName”,
“username”,”password”);
stmt = con.createStatement();
String sql = “DELETE FROM tableName WHERE id = 10”;
stmt.executeUpdate(sql);
System.out.println(“Record deleted successfully”);
} catch (Exception e) {
e.printStackTrace();
} finally {
try{
stmt.close();
con.close();
} catch (Exception e) {
e.printStackTrace();
}
}
}
}
Cassandra – CQL Datatypes
Cassandra supports a variety of data types for column values. The following is a list of the available data types for columns in a Cassandra table:
1. Ascii: A string of characters from the ASCII character set.
2. Bigint: A 64-bit signed long.
3. Blob: A binary large object (BLOB) used to store binary data.
4. Boolean: A Boolean value (true or false).
5. Counter: A counter column type used to store a cumulative value.
6. Decimal: A decimal value with up to 34 digits of precision.
7. Double: A 64-bit IEEE 754-2008 binary floating-point number.
8. Float: A 32-bit IEEE 754-2008 binary floating-point number.
9. Int: A 32-bit signed int.
10. Text: A UTF-8 encoded string.
11. Timestamp: A timestamp value.
12. UUID: A Universally Unique Identifier (UUID).
13. Varint: An arbitrary-precision integer.
14. Timeuuid: A Type-1 UUID, used to store time-based events.
15. List: A list of values of any of the supported data types.
16. Map: A map of values of any of the supported data types.
17. Set: A set of values of any of the supported data types.
Collection Types available in CQL
1. Set: a collection of one or more elements (of the same type) that are unordered and does not contain any duplicates.
2. List: an ordered collection of one or more elements (of the same type) that can contain duplicates.
3. Map: a collection of key-value pairs.
4. Tuples: an ordered collection of one or more elements (of different or same types) that cannot contain duplicates.
5. User-defined types: a collection of related data fields (of different types) that can be used to represent an entity.
User-defined datatypes
User-defined datatypes are specialized structures of data that are created by users to store information in a specific format. These datatypes are designed to store and manipulate data in ways that are not possible with the existing data types provided by programming languages. They are created to store related information in a single unit, allowing for easy retrieval and manipulation. Some examples of user-defined datatypes include linked lists, stacks, queues, trees, and graphs.
Cassandra – CQL Collections
Cassandra is a NoSQL database that provides a variety of data collections and features to help manage data. One of these is the Cassandra Query Language (CQL) collections. CQL collections are a special type of data structure that allow users to store multiple items of the same type in a single column. CQL collections are similar to, but distinct from, other collections such as arrays, lists and sets.
The CQL collections available in Cassandra are as follows:
- Set: A set stores a collection of unique values. It is an unordered collection, meaning that the order of the elements is not preserved. This makes it ideal for storing values such as email addresses or phone numbers, where the order does not matter.
- List: A list stores a collection of values in an ordered sequence. The elements in a list are stored in the order in which they were added. This makes it ideal for storing values such as dates or names, where the order is important.
- Map: A map stores a collection of key-value pairs. It is similar to a dictionary in that each key has a corresponding value. This makes it ideal for storing values such as product names and their prices, or student names and their grades.
- Tuple: A tuple stores a fixed-size collection of values. It is similar to a list in that it can store multiple values in a single column, but unlike a list, it does not allow for the values to be modified after being added. This makes it ideal for storing values such as location coordinates, where the values cannot be changed.
List
A List is an ordered collection of elements. It supports duplicate values and allows for null values. A List is declared when creating a table and is designated by using the keyword list.
For example, to create a table with a list:
CREATE TABLE users (
user_id int PRIMARY KEY,
user_name text,
user_emails list<text>
);
Inserting Data into a List
To insert data into a list, you can use the list.append() method. This will append the given data to the end of the list. For example:
my_list = [1,2,3]
my_list.append(4)
print(my_list)
# Output: [1, 2, 3, 4]
Updating a List
The steps for updating a list are as follows:
1. Identify what needs to be updated.
2. Decide how to update the list.
3. Make the necessary changes.
4. Check that the changes were successfully implemented.
5. Save the updated list.
SET
The following example creates a sample table with two columns, name and phone. For storing multiple phone numbers, we are using set.
Creating a Table with Set
CREATE TABLE contacts
(
name VARCHAR(20),
phone SET(‘mobile’,’landline’,’business’,’home’)
);
Inserting Data into a Set
To add data to a set, use the add() method. This will take one argument, the item to be added to the set. For example:
my_set = set()
my_set.add(1)
my_set.add(2)
my_set.add(‘Hello’)
print(my_set)
# Output: {1, 2, ‘Hello’}
Updating a Set
To update a set, you can use the set methods such as add, update, remove and discard.
You can add an element to a set using the add() method:
s = {1,2,3}
s.add(4)
print(s)
# {1, 2, 3, 4
You can update a set using the update() method and a sequence (list, tuple, string):
s = {1,2,3}
s.update([4,5,6])
print(s)
# {1, 2, 3, 4, 5, 6}
You can remove an element from a set using the remove() or the discard() methods. The remove() method will raise an error if the element is not present in the set, while the discard() method will not.
s = {1,2,3,4,5}
s.remove(4)
print(s)
# {1, 2, 3, 5
You can also use the pop() method to remove an arbitrary element from the set:
s = {1,2,3,4,5}
s.pop()
print(s)
# {2, 3, 4, 5}
Map
Map is a data type that is used to store a key-value pair of elements. It is similar to a dictionary in Python, a hash table in C/C++, or an associative array in Java. It enables the user to quickly retrieve data associated with a specific key.
Creating a Table with Map
1. Log into your MapD account.
2. Click on the “Create” button in the top right corner of the page.
3. Select the option “Table” from the drop-down menu.
4. Enter the name of the table you want to create, and then click “Next”.
5. Enter the table details, such as the number of columns, the data type of each column, and any other settings you want to specify.
6. Once you’ve entered the necessary details, click “Create” to create the table.
7. You should now see the new table listed in the left side panel in the Map interface.
Inserting Data into a Map
To insert data into a Map, you can use the Map’s .set() method and provide it with a key and the data to be stored. For example:
let myMap = new Map();
myMap.set(‘name’, ‘John’);
myMap.set(‘age’, 25);
myMap.set(‘country’, ‘USA’);
Updating a Set
To update a set, you can use the add() and remove() methods to add or remove elements from the set. You can also use the union(), intersection(), difference(), and symmetric_difference() methods to combine multiple sets and update the set.
Cassandra – CQL User Defined Datatypes
Cassandra allows users to define their own datatypes in CQL. User-defined datatypes are useful when defining particular data structures, such as maps or collections, that can be used to store data in a way that is more organized and efficient. User-defined datatypes can be used as a column type in a table, or as part of a composite primary key or clustering column.
User-defined datatypes are defined using the CREATE TYPE command. This command takes two parameters: the name of the datatype and a set of fields that make up the datatype. Each field is specified using a field name, type, and (optionally) a default value. For example, the following command defines a user-defined datatype called “address”:
CREATE TYPE address (
street varchar,
city varchar,
state varchar,
zipcode int
);
Once a user-defined datatype is defined, it can be used in a table definition. For example, the following command creates a table called “customers” that uses the “address” datatype as one of its columns:
CREATE TABLE customers (
customer_id uuid PRIMARY KEY,
name varchar,
address address
);
Once the table is created, data can be inserted into it by providing values for the fields of the address datatype. For example, the following command inserts a row into the customers table:
INSERT INTO customers (customer_id, name, address)
VALUES (uuid(), ‘John Doe’, {street: ‘123 Main St’, city: ‘Springfield’, state: ‘MA’, zipcode: 12345});
Altering a User-defined Data Type
A user-defined data type can be altered by modifying the underlying structure of the data type. This can be done by adding, removing, or modifying the fields, properties, methods, or other components that define the data type. For example, if a user-defined data type is a class that represents an employee, the structure of the class can be altered by adding a new field to store the employee’s address, or by removing an existing field to store the employee’s phone number.
Renaming a Field in a Type
In order to rename a field in a type, you must first open the type in the editor. From there, you can click on the field you want to rename and then click the “Rename” button in the upper-right corner of the editor. Enter the new name for the field and click “OK” to save your changes.
Deleting a User-defined Data Type
To delete a user-defined data type, the user can select the data type in the database and use the DROP command to delete it. For example, if the user has created a type called “MyType” in the database, they can use the following command to delete it: DROP TYPE MyType.