MySQL COUNT（）GROUP BY子查询（？）可以计算每月在多个项目上的购买

Question

I'm using MySQL and i'd like to count the number of purchases of multiple items by the month in which each item was purchased. My table is called "items_purchased", the items are listed by "item_id", and the purchase date is a timestamp called "purchase_date".

here's my query so far:

SELECT items_purchased.item_id, items_purchased.purchase_date, 
DATE_FORMAT(DATE(purchase_date), '%m %y') AS monthYear FROM items_purchased 

The results in plain english would be something like this:

item_id=3: 2 purchases in june 2011, 3 purchases in july 2011
item_id=2: 1 purchase in june 2011, 7 purchases in july 2011

any help to help me figure out how to do the appropriate COUNT() and/or GROUP BY statements (or whatever else i may need) to determine the per month purchases for each item_id would be greatly appreciated!

thank you, tim

Answer 1

SELECT YEAR(purchase_date) as year, DATE_FORMAT(purchase_date, '%M') as month, COUNT(item_id) as cnt
FROM items_purchased
GROUP BY YEAR(purchase_date), MONTH(purchase_date)
ORDER BY year, month, cnt

If you want per-itemID counts, add 'item_id' to the end of the GROUP BY clause. This'll just count how many itemIDs show up in any given year/month, but not break it down per-item.