Cassandra Read Data

Reading data from a Cassandra cluster involves querying the data using the Cassandra Query Language (CQL). CQL is similar to SQL, but with some differences due to the distributed nature of Cassandra. In this tutorial, we’ll cover the basic syntax for reading data in Cassandra, including selecting specific columns, filtering data, and ordering results.

Syntax for Reading Data

The basic syntax for reading data from a Cassandra table is as follows:

SELECT column1, column2, ... FROM table_name WHERE condition;

Here, column1, column2, etc. represent the columns you want to retrieve from the table. table_name is the name of the table you want to read from. WHERE is an optional clause that allows you to filter the results based on certain conditions.

Examples

Let’s look at some examples of how to read data from a table in Cassandra.

1. Selecting all columns

To retrieve all columns from a table, use the following syntax:

SELECT * FROM my_table;

This will return all rows and columns from the my_table table.

2. Selecting specific columns

To retrieve specific columns from a table, list them after the SELECT keyword, separated by commas. For example:

SELECT first_name, last_name, email FROM users;

This will retrieve only the first_name, last_name, and email columns from the users table.

3. Filtering data

You can use the WHERE clause to filter the results based on certain conditions. For example:

SELECT * FROM users WHERE age >= 18;

This will retrieve all rows from the users table where the age column is greater than or equal to 18.

4. Ordering results

You can use the ORDER BY clause to sort the results in ascending or descending order. For example:

SELECT * FROM users ORDER BY last_name ASC;

This will retrieve all rows from the users table and order them by last_name in ascending order.

Reading data in Cassandra involves using CQL to query the database. You can retrieve all columns or specific columns, filter the results based on conditions, and order the results as needed. By using the syntax and examples provided in this tutorial, you should be able to retrieve data from your Cassandra cluster efficiently and effectively.