Add temporary table with index for speeding up consumption graph query

jon/db/add_views.sql

@@ -74,30 +74,40 @@ LEFT JOIN garfield.inventory_items AS b
       AND b.bought > a.bought
 GROUP BY a.item_id;
 
+-- We need to create this table so that we can put an index on it
+-- Otherwise the join in the consumption graph query becomes much slower
+-- Perhaps it would be nicer to use a materialized view instead
+DROP TABLE IF EXISTS last_n_days;
+CREATE TEMPORARY TABLE last_n_days AS (
+  SELECT
+    generate_series(now() - interval '14 days', now(), interval '1 day')::date AS sale_date
+);
+CREATE UNIQUE INDEX last_n_days_sale_date ON last_n_days (sale_date);
+
 -- Get an array of how often items were sold over the last 14 days
 CREATE TEMPORARY VIEW inventory_last_n_days_sales AS
 WITH
-last_n_days AS (
-  SELECT generate_series(now() - interval '14 days', now(), interval '1 day')::date AS sale_date
-),
-last_n_days_sales AS (
+sales_by_date AS (
   SELECT
-    item_id,
-    sale_date,
-    count(snack_sales_log_timestamp) AS sale_date_sales
+    inventory_line AS item_id,
+    date_trunc('day', snack_sales_log_timestamp AT TIME ZONE 'UTC+1') AS sale_date,
+    count(*)::int AS sales
+  FROM garfield.snack_sales_log
+  GROUP BY item_id, sale_date
+),
+beeg AS (
+  SELECT item_id, sale_date, count(snack_sales_log_timestamp)::int AS sales
   FROM garfield.inventory_items
-  LEFT JOIN garfield.inventory_map ON item_id = inventory_id
-  -- Is there a better way of writing this?
-  -- TODO: Try to speed this query up
   CROSS JOIN last_n_days
   LEFT JOIN garfield.snack_sales_log
-         ON inventory_map.snack_id = snack_sales_log.snack_id
-        AND DATE_TRUNC('day', snack_sales_log_timestamp) = sale_date
+         ON inventory_line = item_id
+-- snack_sales_log has an index on snack_sales_log_timestamp to speed up this query
+-- If that index doesn't exist the query takes much longer.
+        AND sale_date = date_trunc('day', snack_sales_log_timestamp AT TIME ZONE 'UTC+1')
+  WHERE available
   GROUP BY item_id, sale_date
   ORDER BY item_id, sale_date
 )
-SELECT
-  item_id,
-  array_agg(sale_date_sales) AS last_n_days_sales
-FROM last_n_days_sales
+SELECT item_id, array_agg(sales) AS last_n_days_sales
+FROM beeg
 GROUP BY item_id