Adding value of COUNT to an already existing value - sql

Question

I have a table for managing inventory movements and a table to manage stock.
I want to add the count of movements that the item exists in between given dates to the stock table.
My update statement looks like this:
UPDATE inventory
SET quantity = quantity + 1
WHERE ItemID IN
( SELECT ItemID FROM movements
WHERE group = '3' AND store = '500'
AND DateMove BETWEEN 20201219 AND 20201223 )
AND StoreNumber = '500'
How can I change this query to add the amount of times that the ItemID appears in movements to the quantity in the inventory table?
I've been thinking that I can add a count(itemID) and group by and add an alias in the subquery and use the alias after the + but it doesn't seem to work.
Thanks for any help

Answer 1

Using an UPDATE, you can use a correlated subquery:
UPDATE inventory i
SET quantity = (i.quantity +
(SELECT COUNT(*)
FROM movements m
WHERE m.ItemId = i.ItemId AND
m.group = 3 AND m.store = i.store AND
m.DateMove BETWEEN 20201219 AND 20201223
)
)
WHERE i.store = 500 AND
EXISTS (SELECT 1
FROM movements m
WHERE m.ItemId = i.ItemId AND
m.group = 3 AND m.store = 500 AND
m.DateMove BETWEEN 20201219 AND 20201223
);
Note that I removed the single quotes around 500 and 3. These values look like numbers. Only use the single quotes if they are strings.
Oracle also allows you to update using a subquery under some circumstances, so this should work as well:
update (select i.*,
(SELECT COUNT(*)
FROM movements m
WHERE m.ItemId = i.ItemId AND
m.group = 3 AND m.store = i.store AND
m.DateMove BETWEEN 20201219 AND 20201223
) as inc_quantity
from inventory i
where store = 500
)
set quantity = quantity + inc_quantity
where quantity > 0;

Answer 2

You appear to want a MERGE statement and to COUNT the movements:
MERGE INTO inventory dst
USING (
SELECT ItemID,
store,
COUNT(*) AS num_movements
FROM movements
WHERE group = 3
AND store = 500
AND DateMove BETWEEN DATE '2020-12-19' AND DATE '2020-12-23'
GROUP BY
ItemId,
store
) src
ON ( src.ItemId = dst.ItemId AND dst.StoreNumber = src.store )
WHEN MATCHED THEN
UPDATE
SET quantity = dst.quantity + src.num_movements;
(Also, if values are numbers then use number literals and not string literals and, for dates, use date literals and not numbers.)

Answer 3

You need a correlated subquery. For brevity, I've omitted all other where conditions.
UPDATE inventory AS inv
SET quantity = quantity + (SELECT COUNT(*) FROM movements AS mov WHERE mov.itemID = inv.itemID);

Answer 4

I think it's better to create a view such as
CREATE OR REPLACE VIEW v_inventory AS
SELECT i.*,
SUM(CASE
WHEN i.StoreNumber = 500 AND m."group" = 3 AND m.store = 500 AND
m.DateMove BETWEEN date'2020-12-19' AND date'2020-12-23'
THEN
1
ELSE
0
END) OVER (PARTITION BY m.ItemID) AS mov_quantity
FROM inventory i
LEFT JOIN movements m
ON m.ItemID = i.ItemID
rather than applying a DML for the sake of good db design, since the desired count already can be calculated, and may yield for later confusions