Why are SQL queries necessary?

SQL queries are necessary for interacting with relational databases. They allow:

• Retrieving data: Getting the required information from tables.
• Inserting data: Adding new records to tables.
• Updating data: Modifying existing records in tables.
• Deleting data: Removing records or entire tables.
• Managing data structure: Creating, modifying, and deleting tables, indexes, and other database objects (DDL - Data Definition Language).
• Managing access: Setting user permissions (DCL - Data Control Language).

For QA specialists, SQL queries are important for:

• Verifying data correctness: Ensuring data is correctly saved in the database after an operation.
• Preparing test data: Creating specific data sets for testing particular scenarios.
• Analyzing test results: Extracting and analyzing data from the database to confirm or refute defects.
• Deep understanding of application operation: Studying how the application interacts with the database.

Examples of simple queries:

-- Retrieve all records from the users table
SELECT *
FROM users;

-- Insert a new record into the products table
INSERT INTO products (name, price)
VALUES ('Laptop', 1200.00);

-- Update the price of the product with id=1
UPDATE products
SET price = 1300.00
WHERE id = 1;

-- Delete the product with id=2
DELETE FROM products
WHERE id = 2;