So I have following data in a product_rate_history table -
I want to select last N records ( eg 7 records ) informing rate change history of given product. If product rate is changed more than one time a day, then query should select most recent rate change for that day.
So from above table I want output like following for product id 16 -
+-----------+-------------------------+------------------------+
| product_id | previous_rate | date |
+----------------+--------------------+------------------------|
| 16 | 2400 | 2016-04-30 23:05:35 |
| 16 | 4500 | 2016-04-29 11:02:42 |
+----------------+--------------------+------------------------+
I have tried following query but it returns only one row having last update rate only-
SELECT * FROM `product_rate_history` prh
INNER JOIN (SELECT max(created_on) as max FROM `product_rate_history` GROUP BY Date(created_on)) prh2
ON prh.created_on = prh2.max
WHERE prh.product_id = 16
GROUP BY DATE(prh.created_on)
ORDER BY prh.created_on DESC;
First, you do not need an aggregation in the outer query.
Second, you need to repeat the WHERE
clause in the subquery (for the method you are using):
SELECT prh.*
FROM product_rate_history prh INNER JOIN
(SELECT max(created_on) as maxco
FROM product_rate_history
WHERE prh.product_id = 16
GROUP BY Date(created_on)
) prh2
ON prh.created_on = prh2.maxco
WHERE prh.product_id = 16
ORDER BY prh.created_on DESC;
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