Use the Describe command to verify whether the table is deleted or not. Since the emp table has been deleted, you will not find it in the column families list.

cqlsh:tecklearn> DESCRIBE COLUMNFAMILIES;

employee

Deleting a Table using Java API

You can delete a table using the execute() method of Session class. Follow the steps given below to delete a table using Java API.

Step1: Create a Cluster Object

First of all, create an instance of Cluster.builder class of com.datastax.driver.core package as shown below −

//Creating Cluster.Builder object

Cluster.Builder builder1 = Cluster.builder();

Add a contact point (IP address of the node) using addContactPoint() method of Cluster.Builder object. This method returns Cluster.Builder.

//Adding contact point to the Cluster.Builder object

Cluster.Builder builder2 = build.addContactPoint( “127.0.0.1” );

Using the new builder object, create a cluster object. To do so, you have a method called build() in the Cluster.Builder class. The following code shows how to create a cluster object.

//Building a cluster

Cluster cluster = builder.build();

You can build a cluster object using a single line of code as shown below.

Cluster cluster = Cluster.builder().addContactPoint(“127.0.0.1”).build();

Step 2: Create a Session Object

Create an instance of Session object using the connect() method of Cluster class as shown below.

Session session = cluster.connect( );

This method creates a new session and initializes it. If you already have a keyspace, you can set it to the existing one by passing the KeySpace name in string format to this method as shown below.

Session session = cluster.connect(“Your keyspace name”);

Here we are using the keyspace named tp. Therefore, create the session object as shown below.

Session session = cluster.connect(“tp”);

Step 3: Execute Query

You can execute CQL queries using execute() method of Session class. Pass the query either in string format or as a Statement class object to the execute() method. Whatever you pass to this method in string format will be executed on the cqlsh.

In the following example, we are deleting a table named emp. You have to store the query in a string variable and pass it to the execute() method as shown below.

// Query

String query = “DROP TABLE emp1;”;

session.execute(query);

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 Drop_Table {

public static void main(String args[]){

//Query

String query = “DROP TABLE emp1;”;

Cluster cluster = Cluster.builder().addContactPoint(“127.0.0.1”).build();

//Creating Session object

Session session = cluster.connect(“tp”);

//Executing the query

session.execute(query);

System.out.println(“Table dropped”);

}

Save the above program with the class name followed by .java, browse to the location where it is saved. Compile and execute the program as shown below.

$javac Drop_Table.java

$java Drop_Table

Under normal conditions, it should produce the following output −

Table dropped

Cassandra – Truncate Table

Truncating a Table

You can truncate a table using the TRUNCATE command. When you truncate a table, all the rows of the table are deleted permanently. Given below is the syntax of this command.

Syntax

TRUNCATE <tablename>

Example

Let us assume there is a table called student with the following data.

s_id	s_name	s_branch	s_aggregate
1	ram	IT	70
2	rahman	EEE	75
3	robbin	Mech	72

When you execute the select statement to get the table student, it will give you the following output.

cqlsh:tp> select * from student;

s_id | s_aggregate | s_branch | s_name

——+————-+———-+——–

1 | 70 | IT | ram

2 | 75 | EEE | rahman

3 | 72 | MECH | robbin

(3 rows)

Now truncate the table using the TRUNCATE command.

cqlsh:tp> TRUNCATE student;

Verification

Verify whether the table is truncated by executing the select statement. Given below is the output of the select statement on the student table after truncating.

cqlsh:tp> select * from student;

s_id | s_aggregate | s_branch | s_name

——+————-+———-+——–

(0 rows)

Truncating a Table using Java API

You can truncate a table using the execute() method of Session class. Follow the steps given below to truncate a table.

Step1: Create a Cluster Object

First of all, create an instance of Cluster.builder class of com.datastax.driver.core package as shown below.

//Creating Cluster.Builder object

Cluster.Builder builder1 = Cluster.builder();

Add a contact point (IP address of the node) using the addContactPoint() method of Cluster.Builder object. This method returns Cluster.Builder.

//Adding contact point to the Cluster.Builder object

Cluster.Builder builder2 = build.addContactPoint( “127.0.0.1” );

Using the new builder object, create a cluster object. To do so, you have a method called build() in the Cluster.Builder class. The following code shows how to create a cluster object.

//Building a cluster

Cluster cluster = builder.build();

You can build a cluster object using a single line of code as shown below.

Cluster cluster = Cluster.builder().addContactPoint(“127.0.0.1”).build();

Step 2: Creating a Session Object

Create an instance of Session object using the connect() method of Cluster class as shown below.

Session session = cluster.connect( );

This method creates a new session and initializes it. If you already have a keyspace, then you can set it to the existing one by passing the KeySpace name in string format to this method as shown below.

Session session = cluster.connect(“ Your keyspace name ” );

Session session = cluster.connect(“ tp” );

Here we are using the keyspace named tp. Therefore, create the session object as shown below.

Step 3: Execute Query

You can execute CQL queries using the execute() method of Session class. Pass the query either in string format or as a Statement class object to the execute() method. Whatever you pass to this method in string format will be executed on the cqlsh.

In the following example, we are truncating a table named emp. You have to store the query in a string variable and pass it to the execute() method as shown below.

//Query

String query = “TRUNCATE emp;;”;

session.execute(query);

Given below is the complete program to truncate a table in Cassandra using Java API.

import com.datastax.driver.core.Cluster;

import com.datastax.driver.core.Session;

public class Truncate_Table {

public static void main(String args[]){

//Query

String query = “Truncate student;”;

//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);

System.out.println(“Table truncated”);

}

Save the above program with the class name followed by .java, browse to the location where it is saved. Compile and execute the program as shown below.

$javac Truncate_Table.java

$java Truncate_Table

Under normal conditions, it should produce the following output −

Table truncated

So, this brings us to the end of blog. This Tecklearn ‘How to Drop and Truncate Tables in Apache Cassandra’ helps you with commonly asked questions if you are looking out for a job in Cassandra and No-SQL Database Domain.

If you wish to learn HBase and build a career in Cassandra or No-SQL Database domain, then check out our interactive, Apache Cassandra Training, that comes with 24*7 support to guide you throughout your learning period. Please find the link for course details:

https://www.tecklearn.com/course/apache-cassandra-training/

Apache Cassandra Training

About the Course

Take your career to the next level as a certified Apache Cassandra developer by acquiring all the skills through our hands-on training sessions. Tecklearn’s Apache Cassandra Certification Training is designed by professionals as per the industry requirements and demands. This Cassandra Certification Training helps you to master the concepts of Apache Cassandra including Cassandra Architecture, its features, Cassandra Data Model, and its Administration. Our Cassandra certification training course lets you master the high availability NoSQL distributed database.

Why Should you take Apache Cassandra Training?

The average salary of a Software Engineer with Apache Cassandra skill is $120,500 per year. – Payscale.com
Cassandra is in use at Constant Contact, CERN, Comcast, eBay, GitHub, GoDaddy, Hulu, Instagram, Intuit, Netflix, Reddit, The Weather Channel, and over 1500 more companies that have large, active data sets.
Apache Cassandra is one of the most widely used NoSQL database. It offers features such as Fault Tolerance, Scalability, Flexible Data Storage and its efficient writes, which makes it the perfect database for various purposes.

What you will Learn in this Course?

Introduction to Big Data, and Cassandra

What is Big Data
Limitations of RDBMS
NoSQL and it’s Characteristics
CAP Theorem
Basic concepts of Cassandra
Features of Cassandra

Cassandra Data model, Installation and setup

Installation of Cassandra
Key concepts and deployment of non-relational database, column-oriented database, Data Model – column, column family

Cassandra Architecture

Explain the Architecture of Cassandra
Different Layers of Cassandra Architecture
Partitioning and Snitches
Explain Vnodes and How Read and Write Path works
Understand Compaction, Anti-Entropy and Tombstone
Describe Repairs in Cassandra

Deep Dive into Cassandra Database

Describe Different Data Types Used in Cassandra
Explain Collection Types
Describe What are CRUD Operations
Implement Insert, Select, Update and D elete of various elements
Implement Various Functions Used in Cassandra
Describe Importance of Roles and Indexing

Backup & Restore and Performance Tuning

Learn backup and restore functionality and its importance
Create a snapshot using Nodetool utility
Restore a snapshot
Understand how to choose the right balance of the following resources: memory, CPU, disks, number of nodes, and network.
Understand all the logs created by Cassandra
Explain the purpose of different log files
Configure the log files
Learn about Performance Tuning
Integration with Spark and Kafka

Advance Modelling

Rules of Cassandra data modelling
Modelling data around queries
Creating table for data queries

Deploying the IDE for Cassandra applications

Learning key drivers
Deploying the IDE for Cassandra applications and cluster connection
Data query implementation

Cassandra Administration

Understanding Node Tool Utility
Cluster management using Command Line Interface
Management and Monitoring using DataStax Ops Center

Cassandra API and Summarization

Cassandra client connectivity
Connection pool internals
Cassandra API
Features and concepts of Hector client
Thrift, JAVA code and Summarization

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