Create a Stored Procedure Debug - mysql

Question

Using the data and schema from this site: Using the data from this site: https://www.sqlservertutorial.net/sql-server-sample-database/
I am given the prompt:
Create a stored procedure called placeOrder() that can be called to insert a new order in the database. It will receive a customerId as an INT, a productId as an INT and a qty as an INT and return (as anoutput parameter) the order_id of the new row created in table orders.
This stored procedure will find the store with the largest stock of that particular product and assign that store to the order. The order_status should be set to 1 (i.e. Pending), the current system date (see function CURDATE) will be assigned to order_date, column required_date will be 7 days from the current system date (see function ADDDATE) and the column staff_id will be assigned for anyone that works in the selected store (per previous requirement). Since the order_id column is not an auto-incremented column you need to calculate the value for it. You can use max(order_id) to find out the highest order_id in the table.
The order_item row shall be set to the productId and qty passed to the stored procedure. The item_id shall be set to 1 (since this order will only have one item).The list price should be retrieved from the products table using the passed productId. The discount value should be set to 0
If I'm understanding the prompt correctly, I need to first the store id which has the most of a particular product. Once I have that store, I need to insert a new row of data into the table "orders" with the essential data being order_id, customer_id, order_status, order_date, required, date, and staff_id. I do NOT understand what the last part of the question is asking/how to go about solving.
Here's my current code, but I'm almost positive it's chalk full of errors and notes and missing pieces so please help me out where you can:
DELIMITER //
CREATE procedure placeOrder (IN customerID INT, IN productID INT, IN QTY INT, OUT order_id INT)
BEGIN
DECLARE customerID INT;
DECLARE produtcID INT;
DECLARE quantity INT;
SELECT customer_id INTO customerID from customers where customer_id = customerID;
SELECT product_id INTO productID from order_items where product_id = productID;
SELECT quantity INTO qty from order_items where quantity = qty;
/**find store id with max stocks of product**/
select st.store_name, sk.store_id from stocks as sk
INNER JOIN
stores as st
ON sk.store_id = st.store_id
WHERE max(sk.quantity)
GROUP by sk.product_id;
select st.store_id from stores as st
INNER JOIN orders as o
ON st.store_id= o.store_id
Insert into orders (order_id, customer_id, order_status, order_date, required_date, staff_id)
WHERE order_status = '1',
AND order_date = select(curdate()),
AND required_date = adddate('order_date' +7),
AND staff_id = /**ANYONE from store listed in precious query (how do I relate these two queries)**
END

Answer 1

Don't re-declare function parameters.
You don't need to use a SELECT query to set variables that are already set in parameters.
You're not getting the store with the maximum quantity correctly. Use ORDER BY sk.quantity DESC LIMIT 1
You need to use INTO <variable> in a query to set variables from a query. If you don't do this, the result of the query will be turned into the result of the procedure, which isn't desired here.
You don't use WHERE in an INSERT statement. WHERE is used for finding existing rows that match a condition, but INSERT is for creating new rows. You use VALUES() to list all the values that should be assigned to the specified columns.
CREATE procedure placeOrder (IN customerID INT, IN productID INT, IN QTY INT, OUT orderId INT)
BEGIN
DECLARE topStoreId INT;
DECLARE staffId INT;
/**find store id with max stocks of product**/
select sk.store_id
from stocks as sk
INNER JOIN stores as st
ON sk.store_id = st.store_id
WHERE sk.product_id = productID
ORDER BY sk.quantity DESC
LIMIT 1
INTO topStoreId;
/* Pick an arbitrary staff from the selected store */
SELECT staff_id
FROM staffs
WHERE store_id = topStoreId
LIMIT 1
INTO staffId;
SELECT MAX(order_id)
FROM orders AS o
INTO orderId;
Insert into orders (order_id, customer_id, order_status, order_date, required_date, staff_id, store_id)
VALUES (orderId, customerId, 1, CURDATE(), DATE_ADD(CURDATE(), INTERVAL 1 WEEK), staffId, topStoreId);
END