What are some advanced SQL exercises I can practice?
Here are a few advanced SQL exercises you can try: 1. Write a query to find the second highest salary in a table. 2. Create a query that returns the top 3 products by sales for each category. 3. Write a recursive query to display a hierarchy of employees.
Can you explain how to find the second highest salary?
Sure! You can use the following SQL query: SELECT MAX(salary) FROM employees WHERE salary < (SELECT MAX(salary) FROM employees);
This will give you the second highest salary.
What about the top 3 products by sales for each category?
You can use a Common Table Expression (CTE) with the ROW_NUMBER() function. Here's an example:
WITH RankedProducts AS (
SELECT product_id, category_id, sales,
ROW_NUMBER() OVER (PARTITION BY category_id ORDER BY sales DESC) as rank
FROM products
)
SELECT * FROM RankedProducts WHERE rank <= 3;
Thanks! Can you give me a recursive query example?
Certainly! Here's a simple recursive query to display an employee hierarchy:
WITH RECURSIVE EmployeeCTE AS (
SELECT employee_id, manager_id, name
FROM employees
WHERE manager_id IS NULL
UNION ALL
SELECT e.employee_id, e.manager_id, e.name
FROM employees e
INNER JOIN EmployeeCTE cte ON e.manager_id = cte.employee_id
)
SELECT * FROM EmployeeCTE;
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