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Introduction to CQL

What is CQL?

CQL, or Cassandra Query Language, is a SQL-like language for querying and managing data in Apache Cassandra, a distributed NoSQL database. CQL is designed to provide a simple and familiar interface for developers who are accustomed to SQL, while also accommodating the unique features and capabilities of Cassandra.

Key Features of CQL

CQL has several key features that distinguish it from traditional SQL:

  • Table-based structure: CQL uses tables to organize data, similar to SQL.
  • No joins: CQL does not support JOIN operations, which are common in relational databases.
  • Flexible data model: CQL allows for flexible schema definitions, enabling developers to add columns as needed.
  • Batch operations: CQL supports batch operations to execute multiple statements at once.

Basic Syntax of CQL

CQL syntax is similar to SQL, which makes it easier for developers to grasp. The basic structure of a CQL command consists of the keywords followed by specific clauses. Here are some examples of common CQL commands:

Creating a Keyspace:

CREATE KEYSPACE my_keyspace WITH REPLICATION = {'class': 'SimpleStrategy', 'replication_factor': 1};

Creating a Table:

CREATE TABLE users (user_id UUID PRIMARY KEY, name text, age int);

Inserting Data:

INSERT INTO users (user_id, name, age) VALUES (uuid(), 'Alice', 30);

Querying Data:

SELECT * FROM users;

Data Types in CQL

CQL supports a variety of data types, which can be categorized as follows:

  • Scalar Types: Includes int, float, double, boolean, text, etc.
  • Collection Types: Includes list, set, and map.
  • UDT (User Defined Types): Custom data types that can be defined by users.
  • UUID: Universally Unique Identifier, useful for distributed systems.

Example of using different data types:

CREATE TABLE products (product_id UUID PRIMARY KEY, name text, price float, tags set);

Conclusion

CQL is a powerful tool for interacting with Cassandra databases, providing a familiar syntax for those experienced with SQL while introducing unique concepts suited to the NoSQL environment. Understanding the basics of CQL will enable you to efficiently manage your data within Cassandra.