What is the most efficient way to select the time where price has increased the max? [Structure at the bottom]
-- get max increased price
select p1.pricetime, max(p2.price) maxnext
from prices p1 inner join prices p2 on p2.id > p1.id
group by p1.pricetime
what is p2.pricetime where p2.price = max(p2.price) for each p1.pricetime?
-- get time of max price
select p3.pricetime, x.maxnext
from prices p3 inner join
(select p1.pricetime, max(p2.price) maxnext
from prices p1 inner join prices p2 on p2.id > p1.id
group by p1.pricetime) x
on x.maxnext = p3.price and p3.id > p1.id
that is a horribly inefficient way for multi million row tables I'm sure you could do something like this in MSSQL :
select p2.pricetime from
(select p1.pricetime, max(p2.price) maxnext
from prices p1 inner join prices p2 on p2.id > p1.id
group by p1.pricetime) x ...
which accesses a subquery alias from outside the subquery?
-- structure :
CREATE TABLE `prices` (
`id` int(11) NOT NULL DEFAULT '0',
`pricetime` varchar(19) DEFAULT NULL,
`price` decimal(10,8) DEFAULT NULL
) ENGINE=InnoDB DEFAULT CHARSET=latin1;
LOCK TABLES `prices` WRITE;
/*!40000 ALTER TABLE `prices` DISABLE KEYS */;
INSERT INTO `prices` (`id`, `pricetime`, `price`)
VALUES
(1,'2014-01-01 21:55:00',1.37622000),
(2,'2014-01-01 21:56:00',1.37616000),
(3,'2014-01-01 21:57:00',1.37616000),
(4,'2014-01-01 21:58:00',1.37498000),
(5,'2014-01-01 21:59:00',1.37529000),
(6,'2014-01-01 22:03:00',1.37518000),
(7,'2014-01-01 22:05:00',1.37542000),
(8,'2014-01-01 22:06:00',1.37558000),
(9,'2014-01-01 22:07:00',1.37560000),
(10,'2014-01-01 22:08:00',1.37560000);
/*!40000 ALTER TABLE `prices` ENABLE KEYS */;
UNLOCK TABLES;
Thanks Gordon, when I asked the question stackoverflow suggested correlated-subquery as a tag. Therein lied the answer. So here goes :
The time of maximum increase :
SELECT p1.pricetime starttime, min(p4.pricetime) endtime,
p1.price startingprice, p4.price maxnextprice
FROM prices p1 inner join prices p4 on p4.id > p1.id
WHERE p4.price =
(SELECT max(p3.price)
FROM prices p2 inner join prices p3 on p3.id > p2.id
where p1.id = p2.id
group by p2.pricetime order by max(p3.price) limit 1)
group by p1.pricetime, p4.price;
Thanks for your input.