mysql query using aggregate function to select field values - mysql

Question

MySQL 5.5.29
Here is a mysql query I am working on without success:
SELECT ID, Bike,
(SELECT IF( MIN( ABS( DATEDIFF( '2011-1-1', Reading_Date ) ) ) = ABS( DATEDIFF( '2011-1-1', Reading_Date ) ) , Reading_Date, NULL ) FROM odometer WHERE Bike=10 ) AS StartDate,
(SELECT IF( MIN( ABS( DATEDIFF( '2011-1-1', Reading_Date ) ) ) = ABS( DATEDIFF( '2011-1-1', Reading_Date ) ) , Miles, NULL ) FROM odometer WHERE Bike=10 ) AS BeginMiles,
(SELECT IF( MIN( ABS( DATEDIFF( '2012-1-1', Reading_Date ) ) ) = ABS( DATEDIFF( '2012-1-1', Reading_Date ) ) , Reading_Date, NULL ) FROM odometer WHERE Bike=10 ) AS EndDate,
(SELECT IF( MIN( ABS( DATEDIFF( '2012-1-1', Reading_Date ) ) ) = ABS( DATEDIFF( '2012-1-1', Reading_Date ) ) , Miles, NULL ) FROM odometer WHERE Bike=10 ) AS EndMiles
FROM `odometer`
WHERE Bike =10;
And the result is:
ID Bike StartDate BeginMiles EndDate EndMiles
14 10 [->] 2011-04-15 27.0 NULL NULL
15 10 [->] 2011-04-15 27.0 NULL NULL
16 10 [->] 2011-04-15 27.0 NULL NULL
Motocycle owners enter odometer readings once a year at or near January 1. I want to calculate the total mileage by motorcycle.
Here is what the data in the table odometer looks like:
(source: bmwmcindy.org)
So to calculate the mileage for this bike for 2011, I need determine which of these records is closer to Jan. 1, 2011 and that is record 14. The starting mileage would be 27. I need to find the record closest to Jan. 1, 2012 and that is record 15. The ending mileage for 2011 is 10657 (which will also be the starting odometer reading when 2012 is calculated.
Here is the table:
DROP TABLE IF EXISTS `odometer`;
CREATE TABLE IF NOT EXISTS `odometer` (
`ID` int(3) NOT NULL AUTO_INCREMENT,
`Bike` int(3) NOT NULL,
`is_MOA` tinyint(1) NOT NULL,
`Reading_Date` date NOT NULL,
`Miles` decimal(8,1) NOT NULL,
PRIMARY KEY (`ID`),
KEY `Bike` (`Bike`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8 AUTO_INCREMENT=22 ;
data for table odometer
INSERT INTO `odometer` (`ID`, `Bike`, `is_MOA`, `Reading_Date`, `Miles`) VALUES
(1, 1, 0, '2012-01-01', 5999.0),
(2, 6, 0, '2013-02-01', 14000.0),
(3, 7, 0, '2013-03-01', 53000.2),
(6, 1, 1, '2012-04-30', 10001.0),
(7, 1, 0, '2013-01-04', 31000.0),
(14, 10, 0, '2011-04-15', 27.0),
(15, 10, 0, '2011-12-31', 10657.0),
(16, 10, 0, '2012-12-31', 20731.0),
(19, 1, 1, '2012-09-30', 20000.0),
(20, 6, 0, '2011-12-31', 7000.0),
(21, 7, 0, '2012-01-03', 23000.0);
I am trying to get dates and miles from different records so that I can subtact the beginning miles from the ending miles to get total miles for a particular bike (in the example Bike=10) for a particular year (in this case 2011).
I have read quite a bit about aggregate functions and problems of getting values from the correct record. I thought the answer is somehow in a subqueries. But when try the query above I get data from only the first record. In this case the ending miles should come from the second record.
I hope someone can point me in the right direction.

Answer 1

Miles should be steadily increasing. It would be nice if something like this worked:
select year(Reading_Date) as yr,
max(miles) - min(miles) as MilesInYear
from odometer o
where bike = 10
group by year(reading_date)
Alas, your logic is really much harder than you think. This would be easier in a database such as SQL Server 2012 or Oracle that has the lead and lag functions.
My approach is to find the first and last reading dates for each year. You can calculate this using a correlated subquery:
select o.*,
(select max(date) from odometer o2 where o.bike = o2.bike and o2.date <= o.date - dayofyear(o.date) + 1
) ReadDateForYear
from odometer o
Next, summarize this at the bike and year levels. If there is no read date for the year one or before the beginning of the year, use the first date:
select bike, year(date) as yr,
coalesce(min(ReadDateForYear), min(date)) as FirstReadDate,
coalesce(min(ReadDateForNextYear), max(date)) as LastReadDate
from (select o.*,
(select max(date) from odometer o2 where o.bike = o2.bike and o2.date <= o.date - dayofyear(o.date) + 1
) ReadDateForYear,
(select max(date) from odometer o2 where o.bike = o2.bike and o2.date <= date_add(o.date - dayofyear(0.date) + 1 + interval 1 year)
) ReadDateForNextYear
from odometer o
) o
group by bike, year(date)
Let me call this . To get the final results, you need something like:
select the fields you need
from <q> q join
odometer s
on s.bike = q.bike and year(s.date) = q.year join
odometer e
on s.bike = q.bike and year(e.date) = q.year
Note: this SQL is untested. I'm sure there are syntax errors.