Question

I have a query that I’d like to change so that it gives me the counts for the current 52 weeks. This query makes use of a calendar table I’ve made which contains a list of dates in a fixed range. The query as it stands is selecting max and min dates and not necessarily the last 52 weeks.

I’m wondering how to keep my calendar table current such that I can get the last 52-weeks (i.e, from right now to one year ago). Or is there another way to make the query independent of using a calendar table?

Here’s the query:

SELECT calendar.datefield AS date, IFNULL(SUM(purchaseyesno),0) AS item_sales
FROM items_purchased join items on items_purchased.item_id=items.item_id 
RIGHT JOIN calendar ON (DATE(items_purchased.purchase_date) = calendar.datefield)
WHERE (calendar.datefield BETWEEN (SELECT MIN(DATE(purchase_date)) 
FROM items_purchased) AND (SELECT MAX(DATE(purchase_date)) FROM items_purchased)) 
GROUP BY week(date)

thoughts?

Answer 1

Some people dislike this approach but I tend to use a dummy table that contains values from 0 – 1000 and then use a derived table to produce the ranges that are needed –

CREATE TABLE dummy (`num` INT NOT NULL);
INSERT INTO dummy VALUES (0), (1), (2), (3), (4), (5), .... (999), (1000);

If you have a table with an auto-incrementing id and plenty of rows you could generate it from that –

CREATE TABLE `dummy`
SELECT id AS `num` FROM `some_table` WHERE `id` <= 1000;

Just remember to insert the 0 value.

SELECT CURRENT_DATE - INTERVAL num DAY
FROM dummy
WHERE num < 365

So, applying this approach to your query you could do something like this –

SELECT WEEK(calendar.datefield) AS `week`, IFNULL(SUM(purchaseyesno),0) AS item_sales
FROM items_purchased join items on items_purchased.item_id=items.item_id 
RIGHT JOIN (
    SELECT (CURRENT_DATE - INTERVAL num DAY) AS datefield
    FROM dummy
    WHERE num < 365
) AS calendar ON (DATE(items_purchased.purchase_date) = calendar.datefield)
WHERE calendar.datefield >= (CURRENT_DATE - INTERVAL 1 YEAR)
GROUP BY week(datefield) -- shouldn't this be datefield instead of date?