1. Filtering Based on Aggregated Data:

• Retrieve rows based on aggregated data, like finding employees with salaries above the average.

SELECT employee_name
FROM employees
WHERE salary > (SELECT AVG(salary) FROM employees);

2. Nested Aggregations:

• Nesting aggregates, such as finding employees with salaries above the average salary in their department.

SELECT employee_name
FROM employees
WHERE salary > (SELECT AVG(salary) FROM employees);

3. Existence Check:

• Check for the existence of records meeting certain conditions.

SELECT product_name
FROM products
WHERE EXISTS (SELECT 1 FROM orders WHERE orders.product_id = products.product_id);

4. Finding Maximum or Minimum Value:

• Retrieve rows with the maximum or minimum value in a column.

SELECT employee_name
FROM employees
WHERE salary = (SELECT MAX(salary) FROM employees);

5. Subquery in the FROM Clause:

• Using a subquery in the FROM clause to create a derived table.

SELECT department_name…