Add support for adding 'loose' items to transactions

Groceries.Data/Migrations/20241012012628_transaction_items_unit.sql

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+DROP VIEW item_purchases;
+DROP VIEW transaction_totals;
+
+ALTER TABLE transaction_items
+    ALTER COLUMN quantity TYPE numeric(5, 3);
+
+ALTER TABLE transaction_items
+    ADD COLUMN IF NOT EXISTS unit text;
+
+CREATE VIEW item_purchases AS
+SELECT
+    item_id,
+    transaction_id,
+    created_at,
+    store_id,
+    price,
+    quantity,
+    unit,
+    CASE ROW_NUMBER() OVER (PARTITION BY item_id ORDER BY created_at DESC)
+        WHEN 1 THEN true
+        ELSE false
+    END AS is_last_purchase
+FROM transaction_items
+JOIN transactions USING (transaction_id);
+
+CREATE VIEW transaction_totals AS
+SELECT transaction_id, sum(amount) AS total
+FROM (
+    SELECT transaction_id, price * quantity AS amount
+    FROM transaction_items
+    UNION ALL
+    SELECT transaction_id, -amount
+    FROM transaction_promotions
+) AS transaction_amounts
+GROUP BY transaction_id;