SQL Test 5

What is the difference between NULL and 0?

What is AUTO_INCREMENT/IDENTITY and which data types support it?

What are the different ways to use INSERT command?

How does GROUP BY handle NULL values?

How does ORDER BY work with SELECT statement?

When should indexes be dropped or rebuilt?

How can multiple SQL operators be combined effectively?

Can WHERE clause be used with INNER JOIN?

When should OUTER JOINs be used instead of INNER JOINs?

How do aggregate functions handle NULL values?

Which query counts the total number of students in the students table?

In an employees table with columns (emp_id INT, salary DECIMAL(10,2), hire_date DATE, is_active BOOLEAN), write a query to show employee ID and years of service for active employees hired before 2020.

Delete all products with zero stock quantity from products table, then completely remove the temp_backup table from the database.

From an orders table (order_id, customer_id, order_date, total_amount), find the total sales amount and number of orders for each customer.

From a products table (product_id, product_name, category, price, stock_quantity), select product_name as 'Product', price as 'Cost' for products in categories 'Electronics', 'Books', or 'Clothing' where stock is greater than 0.

You have an index on the last_name column of the customers table. Why might the following query not use that index?
SELECT * FROM customers WHERE UPPER(last_name) = 'SMITH';

From a orders table (order_id, customer_id, order_date, status, total_amount), find orders that are NOT in status 'Cancelled' or 'Refunded', have total amount between $50 and $200, and customer_id is NOT in the list (101, 102, 103).

Using the orders (order_id, customer_id, total_amount) and customers (customer_id, country) tables, find the total sales amount for each country.

Using a LEFT OUTER JOIN between customers and orders, you want to find only those customers who have not placed any orders.

Which query shows the minimum and maximum salary from the employees table?