SQL Selcting Multiple Tables Commands

Question 1

What does the command Nested SELECT do and give example

Answer 1

A select within another select statement (nested). A mini select within the main one

Example:

SELECT * FROM users WHERE age > (SELECT AVG(age) FROM users);

(retrieves users with an age greater than the average age)

Question 2

What does the command JOIN do and give an example

Answer 2

Combines data from two or more tables based on a related column

Example:

SELECT users.name, orders.order_id FROM users
JOIN orders
ON users.user_id = orders.user_id;
(retrieves user names and their corresponding order IDs)