In this short tutorial we'll discuss cqlsh, what it is and how to use it.
cqlsh is a command line shell for interacting with Cassandra, a distributed database management system. It allows you to execute Cassandra Query Language (CQL) commands and perform database operations on Cassandra.
Cassandra Query Language (CQL) is the primary language for interacting with Cassandra and is similar to Structured Query Language (SQL), which is the common language for interacting with relational database management systems (RDBMS).
However, there are some differences between CQL and SQL:
- CQL is designed specifically for Cassandra, while SQL is a more general-purpose language. As a result, CQL includes some features that are specific to Cassandra, such as support for distributed data and data replication.
- CQL uses a different syntax and data model than SQL. For example, CQL uses a variation of the SQL SELECT statement called SELECT, but the syntax is a bit different. Also, CQL uses a concept called a "column family" instead of tables, and rows are organized differently in CQL than in SQL.
- Cassandra is a NoSQL database, which means it does not use a relational model. That means that CQL does not support some features that are commonly found in SQL, such as JOIN clauses and subqueries.
2. How to use cqlsh
To use cqlsh, we need to have Cassandra installed and running on our system. Once we have Cassandra installed, we can start the cqlsh shell by simply running the "cqlsh" command in our terminal and we'll see cqlsh prompt where we can type CQL commands. If you're getting the error that says that cqlsh is not recognized as a command, please assure that the Cassandra installation folder that contains cqlsh is present in your Path.
Here are some basic commands we can use in cqlsh:
DESCRIBE KEYSPACES: Shows a list of all keyspaces that are available in the current Cassandra cluster.
USE my_keyspace_name: switches to the specified keyspace.
DESCRIBE TABLES: Shows a list of all tables in the current keyspace.
SELECT * FROM table_name: Retrieves all rows from the specified table.
In this short tutorial, we explained what cqlsh is and how to use it to run CQL commands on our Cassandra cluster.