Data Manipulation Language (DML) in CQL
What is Data Manipulation Language (DML)?
Data Manipulation Language (DML) is a subset of SQL (Structured Query Language) used for managing data within a database. In the context of Cassandra, a NoSQL database, DML is used to insert, update, delete, and select data from tables. DML commands allow users to manipulate the data stored in the database effectively, enabling dynamic and flexible data management.
CQL DML Commands
In Cassandra, the primary DML commands are INSERT, UPDATE, DELETE, and SELECT. Each of these commands serves a specific purpose in data manipulation.
1. INSERT Command
The INSERT command is used to add new rows of data into a table. If a row with the same primary key already exists, the existing row will be updated with the new values.
INSERT INTO users (user_id, name, age) VALUES (1, 'John Doe', 30);
This command inserts a new user with user_id 1, name 'John Doe', and age 30 into the users table.
2. UPDATE Command
The UPDATE command modifies existing data within a table. It allows you to change the values of a specific row identified by its primary key.
UPDATE users SET age = 31 WHERE user_id = 1;
This command updates the age of the user with user_id 1 to 31 in the users table.
3. DELETE Command
The DELETE command removes rows from a table. You must specify which rows to delete by using the primary key.
DELETE FROM users WHERE user_id = 1;
This command deletes the user with user_id 1 from the users table.
4. SELECT Command
The SELECT command retrieves data from a table. You can specify which columns to retrieve and apply conditions to filter results.
SELECT name, age FROM users WHERE user_id = 1;
This command retrieves the name and age of the user with user_id 1 from the users table.
Conclusion
Data Manipulation Language (DML) is essential for interacting with the data stored in Cassandra. By mastering the INSERT, UPDATE, DELETE, and SELECT commands, users can efficiently manage and manipulate their data. Understanding these commands enables developers to build dynamic applications that rely on effective data management.