Blog

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.

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