What alternative is used instead of a nested subquery in SQL queries with JOIN?

Using JOIN in SQL serves as an alternative to nested subqueries for combining data from multiple tables. Instead of executing subqueries, which can be less efficient and harder to optimize, JOINs directly relate tables based on keys.

For example, instead of:

SELECT * FROM orders WHERE customer_id IN (SELECT id FROM customers WHERE country = 'USA');

You can write:

SELECT orders.* FROM orders
JOIN customers ON orders.customer_id = customers.id
WHERE customers.country = 'USA';

Advantages of using JOIN:

• Improved readability and maintainability of code.
• Often more efficient query execution, as the database optimizer handles JOINs better.
• Ability to select and filter data from multiple tables simultaneously.

Thus, JOIN is a structured way to combine tables, replacing nested subqueries for better performance and convenience.