Query date column from join table - mysql

Question

Here is the schema:
Customer (Customer_ID, Name, Address, Phone),
Porder (Customer_ID, Pizza_ID, Quantity, Order_Date),
Pizza (Pizza_ID, Name, Price).
I want to get all customers that ordered a pizza in the last 30 days, based on the Order_Date & who spent the most money in the last 30 days. Can these be combined into one?
Here is what I am trying and I am not sure about DATEDIFF or how the query would calculate the total money.
SELECT customer.customer_ID, customer.name FROM customer
JOIN porder ON customer.customer_ID = porder.customer_ID
GROUP BY customer.customer_ID, customer.name
WHERE DATEDIFF(porder.porder_date,getdate()) between 0 and 30
Who spent the most money last 30 days?
SELECT porder.customer_ID, porder.pizza_id, porder.quantity FROM order
JOIN pizza ON porder.pizza_ID = pizza.pizza_ID
GROUP BY porder.customer_ID
WHERE MAX((porder.quantity * pizza.price)) && DATEDIFF(porder.porder_date,getdate()) between 0 and 30

Answer 1

Remember that functions are blackboxes to query optimizer, so you better make the query fit the index, and not the other way around.
WHERE DATEDIFF(order.order_date,getdate()) between 0 and 30
can be rewritten, so that the query would use plain index on order_date
WHERE order.order_date >= CURRENT_DATE - INTERVAL 30 DAY
Who spent the most money in the last 30 days
SELECT
o.customer_id, SUM(p.price * o.quantity)
FROM
order o
INNER JOIN pizza p
ON o.pizza_id = p.pizza_id
WHERE
order_date >= CURRENT_DATE - INTERVAL 30 DAY
GROUP BY o.customer_id
ORDER BY SUM(p.price * o.quantity) DESC
LIMIT 1

Answer 2

Something to think about once you've sorted out your tables, and separated order details from orders.
SELECT * FROM ints;
+---+
| i |
+---+
| 0 |
| 1 |
| 2 |
| 3 |
| 4 |
| 5 |
| 6 |
| 7 |
| 8 |
| 9 |
+---+
SELECT x.*
, IF(x.i = y.maxi,1,0) is_biggest
FROM ints x
LEFT
JOIN (SELECT MAX(i) maxi FROM ints) y
ON y.maxi = x.i;
+---+------------+
| i | is_biggest |
+---+------------+
| 0 | 0 |
| 1 | 0 |
| 2 | 0 |
| 3 | 0 |
| 4 | 0 |
| 5 | 0 |
| 6 | 0 |
| 7 | 0 |
| 8 | 0 |
| 9 | 1 |
+---+------------+