Fixed per unit stock grocycodes weren't unique per unit (fixes #1676)

migrations/0156.sql

@@ -0,0 +1,21 @@
+DROP VIEW stock_splits;
+CREATE VIEW stock_splits
+AS
+
+/*
+	Helper view which shows splitted stock rows which could be compacted
+	(a stock_id starting with "x" indicates that this entry shouldn't be compacted)
+*/
+
+SELECT
+	product_id,
+	SUM(amount) AS total_amount,
+	MIN(stock_id) AS stock_id_to_keep,
+	MAX(id) AS id_to_keep,
+	GROUP_CONCAT(id) AS id_group,
+	GROUP_CONCAT(stock_id) AS stock_id_group,
+	id -- Dummy
+FROM stock
+WHERE stock_id NOT LIKE 'x%'
+GROUP BY product_id, best_before_date, purchased_date, price, open, opened_date, location_id, shopping_location_id
+HAVING COUNT(*) > 1;