MySQL按最后记录的日期过滤

Question

I have two tables with the following structure:

Table items:

 - id (int)

Table item_events:

 - item_id (int)
 - created_at (DateTime)

Each item can have zero, one or more item_events. I need to find all the items whose last item_event was created between two specific dates. Up to know I have built the following SQL query:

SELECT DISTINCT `items`.* 
FROM `items` INNER JOIN `item_events` ON `items`.`id` = `item_events`.`item_id` 
WHERE (item_events.created_at >= '2016-01-01 00:00:00') AND (item_events.created_at <= '2016-01-05 23:59:59');

However, this query is selecting any item that has an item_event between the given dates, even though this item_event is not the last one related to the item. Any help would be appreciated.

Answer 1

You can use a derived table that contains the latest created_at value per item_id :

SELECT `items`.* 
FROM `items` 
INNER JOIN (
   SELECT `item_id`, MAX(`created_at`) AS `created_at`
   FROM `item_events`
   GROUP BY `item_id`
) AS `item_events` ON `items`.`id` = `item_events`.`item_id` 
WHERE (item_events.created_at >= '2016-01-01 00:00:00') AND
      (item_events.created_at <= '2016-01-05 23:59:59');