SQL to reconcile two tables - sql

Question

I have two tables ItemSold and ItemInventory, and am trying to create a query that will check if the ItemSold SUM(quantity of an item) is balanced against ItemInventory.
ItemSold
sale_id | item_id | quantity | conversion |
-------- ------- --------- ----------
1099 1 1.00 1.00
1099 1 1.00 0.50
1099 2 1.00 1.00
I'm using the conversion column to signify a retail/smaller unit of an item
ItemInventory
id | description | quantity
----- ------------ --------
1 Item1 100.00
2 Item2 100.00
Below is a query that I created to check if there are items that if you SUM up is greater than the quantity on the ItemInventory.
SELECT ItemSold.item_id, ItemSold.quantity, ItemSold.conversion
FROM ItemSold
INNER JOIN ItemInventory
ON ItemSold.item_id = ItemInventory.id
WHERE Itemsold.sale_id = #saleid
GROUP BY ItemSold.item_id, ItemSold.quantity, ItemSold.conversion
HAVING SUM(ItemSold.quantity * ItemSold.conversion) > SUM(ItemInventory.quantity)
It works but it compares the quantity of EACH ROW on the ItemSold rather than the SUM(quantity group by item_id).
My goal is to not process the Sale transaction unless there is enough inventory regardless what unit the item is sold.

Answer 1

The strategy of this query is to aggregate, for each item, the total quantity promised to be sold in the ItemSold table, and then compare this number against the inventory number which is available. Items not having sufficient quantity are displayed in the result set.
SELECT t1.id,
t1.description
FROM ItemInventory t1
LEFT JOIN
(
SELECT item_id, SUM(quantity*conversion) AS quantity_sold
FROM ItemSold
GROUP BY item_id
) t2
ON t1.id = t2.item_id
WHERE t1.quantity < COALESCE(t2.quantity_sold, 0)

Answer 2

This will check that all the items are in the inventory for the sale_id of 1099:
SELECT sale_id,
MIN( CASE WHEN s.total_quantity <= i.quantity THEN 1 ELSE 0 END )
AS can_process_order
FROM ( SELECT sale_id,
item_id,
SUM( quantity ) AS total_quantity
FROM itemsold
WHERE sale_id = 1099
GROUP BY sale_id, item_id
) s
LEFT OUTER JOIN
iteminventory i
ON ( s.item_id = i.id )
GROUP BY sale_id;
It will output 1 if there are sufficient items and 0 if any one item does not have enough stock.
To perform the update you can do:
MERGE INTO iteminventory dst
USING (
SELECT i.ROWID AS rid,
total_sale,
MIN( CASE WHEN total_sale <= quantity THEN 1 ELSE 0 END )
OVER ( PARTITION BY sale_id ) AS can_process_sale
FROM (
SELECT sale_id,
item_id,
SUM( quantity ) AS total_sale
FROM itemsold
WHERE sale_id = 1099
GROUP BY sale_id, item_id
) s
LEFT OUTER JOIN iteminventory i
ON ( i.id = s.item_id )
) src
ON ( src.rid = dst.ROWID AND src.can_process_sale = 1 )
WHEN MATCHED THEN
UPDATE SET quantity = quantity - total_sale;