Page 43 - SQL

RosterEnd,
CASE TeamA WHEN 1 THEN 'RR' WHEN 2 THEN 'DS' WHEN 3 THEN 'NS' END AS TeamA,
CASE TeamB WHEN 1 THEN 'RR' WHEN 2 THEN 'DS' WHEN 3 THEN 'NS' END AS TeamB,
CASE TeamC WHEN 1 THEN 'RR' WHEN 2 THEN 'DS' WHEN 3 THEN 'NS' END AS TeamC
FROM roster

Result

I.e. For Week 1 TeamA is on R&R, TeamB is on Day Shift and TeamC is on Night Shift.

Refactoring a query to use Common Table Expressions

Suppose we want to get all product categories with total sales greater than 20.

Here is a query without Common Table Expressions:

SELECT category.description, sum(product.price) as total_sales
FROM sale
LEFT JOIN product on sale.product_id = product.id
LEFT JOIN category on product.category_id = category.id
GROUP BY category.id, category.description
HAVING sum(product.price) > 20

And an equivalent query using Common Table Expressions:

WITH all_sales AS (
SELECT product.price, category.id as category_id, category.description as
category_description
FROM sale
LEFT JOIN product on sale.product_id = product.id
LEFT JOIN category on product.category_id = category.id
)
, sales_by_category AS (
SELECT category_description, sum(price) as total_sales
FROM all_sales
GROUP BY category_id, category_description
)
SELECT * from sales_by_category WHERE total_sales > 20

Example of a complex SQL with Common Table Expression

Suppose we want to query the "cheapest products" from the "top categories".

Here is an example of query using Common Table Expressions

https://riptutorial.com/ 25