making a query for stock/price trend in mysql - mysql

Question

SQL Fiddle
Table scheme:
CREATE TABLE company
(`company_id` int,`name` varchar(30))
;
INSERT INTO company
(`company_id`,`name`)
VALUES
(1,"Company A"),
(2,"Company B")
;
CREATE TABLE price
(`company_id` int,`price` int,`time` timestamp)
;
INSERT INTO price
(`company_id`,`price`,`time`)
VALUES
(1,50,'2015-02-21 02:34:40'),
(2,60,'2015-02-21 02:35:40'),
(1,70,'2015-02-21 05:34:40'),
(2,120,'2015-02-21 05:35:40'),
(1,150,'2015-02-22 02:34:40'),
(2,130,'2015-02-22 02:35:40'),
(1,170,'2015-02-22 05:34:40'),
(2,190,'2015-02-22 05:35:40')
I'm using Cron Jobs to fetch company prices. In concatenating the price history for each company, how can I make sure that only the last one in each day is included? In this case, I want all of the price records around 05:30am concatenated.
This is the result I'm trying to get (I have used Date(time) to only get the dates from the timestamps):
COMPANY_ID PRICE TIME
1 70|170 2015-02-21|2015-02-22
2 120|190 2015-02-21|2015-02-22
I have tried the following query but it doesn't work. The prices don't correspond to the dates and I don't know how to exclude all of the 2:30 am records before applying the Group_concat function.
SELECT company_id,price,trend_date FROM
(
SELECT company_id, GROUP_CONCAT(price SEPARATOR'|') AS price,
GROUP_CONCAT(trend_date SEPARATOR'|') AS trend_date
FROM
(
SELECT company_id,price,
DATE(time) AS trend_date
FROM price
ORDER BY time ASC
)x1
GROUP BY company_id
)t1
Can anyone show me how to get the desired result?

Answer 1

Ok, so this should work as intended:
SELECT p.company_id,
GROUP_CONCAT(price SEPARATOR '|') as price,
GROUP_CONCAT(PriceDate SEPARATOR '|') as trend_date
FROM price as p
INNER JOIN (SELECT company_id,
DATE(`time`) as PriceDate,
MAX(`time`) as MaxTime
FROM price
GROUP BY company_id,
DATE(`time`)) as t
ON p.company_id = t.company_id
AND p.`time` = t.MaxTime
GROUP BY p.company_id
Here is the modified sqlfiddle.

Answer 2

This is a bit unorthodox but I think it solves your problem:
SELECT company_id,
GROUP_CONCAT(price SEPARATOR'|'),
GROUP_CONCAT(trend_date SEPARATOR'|')
FROM (
SELECT *
FROM (
SELECT company_id,
DATE(`time`) `trend_date`,
price
FROM price
ORDER BY `time` DESC
) AS a
GROUP BY company_id, `trend_date`
) AS b
GROUP BY company_id