How to select array of rows with max param from each range? - mysql

Question

I have sqlite table like so:
CREATE TABLE "table" (
`id` INTEGER NOT NULL PRIMARY KEY AUTOINCREMENT UNIQUE,
`param` REAL NOT NULL,
`date` INTEGER NOT NULL
);
INSERT INTO table (param , date) VALUES (123.3, 1427824800 );
INSERT INTO table (param , date) VALUES (122.3, 1427825800 );
INSERT INTO table (param , date) VALUES (125.0, 1427652000 );
INSERT INTO table (param , date) VALUES (123.9, 1427652900);
|id| param | date |
|==|=======|============|
| 1| 123.3 | 1427824800 |
| 2| 122.3 | 1427825800 |
| 3| 125 | 1427652000 |
| 4| 123.9 | 1427652900 |
And get row with max date for each day like(BETWEEN startDay AND endDay) - I need to understand how to group it at least by day, but if there are any way to group via custom period(week, month) it would be great
SELECT id, param, MAX(date) FROM table WHERE date BETWEEN 1427652000 AND 1427824799
SELECT id, param, MAX(date) FROM table WHERE date BETWEEN 1427824800 AND 1427911199
But trully I got much more data for nearly year and 1000+ rows and make 365 queries not an option I think, but I don't know how to optimize it
UPD
After all I think it is real to get one query to get result like this:
|id| param | date |
|==|=======|============|
| 2| 122.3 | 1427825800 |
| 4| 123.9 | 1427652900 |

Answer 1

Here's what you want. You'll use GROUP BY and you'll use the DATE() function to extract the day from each item. UNIX_TIMESTAMP() and FROM_UNIXTIME() are helpful for flipping back and forth between the TIMESTAMP and DATETIME representations. This is necessary because the date arithmetic stuff works on DATETIME values. CURDATE() means today.
SELECT DATE(FROM_UNIXTIME(`date`)) AS day,
MAX(`date`) AS latest_timestamp_in_day
FROM table
WHERE `date` >= UNIX_TIMESTAMP(CURDATE() - INTERVAL 366 DAY)
AND `date` < UNIX_TIMESTAMP(CURDATE())
GROUP BY DATE(FROM_UNIXTIME(`date`))
ORDER BY DATE(FROM_UNIXTIME(`date`)) DESC
This works because
DATE(FROM_UNIXTIME(`date`))
takes each timestamp and returns the DATETIME value of the first moment of the calendar day in which it falls.
The first WHERE clause picks up dates on or after a year and a day ago. The second one excludes today's dates; presumably the MAX operation doesn't make much sense on a not-yet-completed day.
It isn't clear from your question whether you also want to display the param value associated with the last timestamp in each calendar day. If you do, that's a little harder. You first need to get the latest timestamp in each day, then you need to pull out the detail record. That requires a join operation. You'll treat the above query as a subquery, and join it to your table. Like this.
SELECT summary.day, detail.`date`, detail.param
FROM table AS detail
JOIN (
SELECT DATE(FROM_UNIXTIME(`date`)) AS day,
MAX(`date`) AS latest_timestamp_in_day
FROM table
WHERE `date` >= UNIX_TIMESTAMP(CURDATE() - INTERVAL 366 DAY)
AND `date` < UNIX_TIMESTAMP(CURDATE())
GROUP BY DATE(FROM_UNIXTIME(`date`))
) AS summary ON detail.`date` = summary.latest_timestamp_in_day
ORDER BY summary.day DESC
Careful, though. the DATETIME arithmetic is done in the local time zone. This can lead to bizarre results on the days when local time changes from daylight savings to standard and back.
Notice that your column named date is in backticks. It's the same as a reserved word in MySQL's query language, so the backticks help disambiguate.
Here's a more detailed exposition of this business of grouping by date. http://www.plumislandmedia.net/mysql/sql-reporting-time-intervals/

Answer 2

You can use a generator to generate each year day and then join with your table:
SELECT r0 as start_day, MAX(date)
(
SELECT #row as r0, #row := #row + (24*60*60) as r1 FROM
(select 0 union all select 1 union all select 3 union all
select 4 union all select 5 union all select 6 union all
select 6 union all select 7 union all select 8 union all select 9) st1,
(select 0 union all select 1 union all select 3 union all
select 4 union all select 5 union all select 6 union all
select 6 union all select 7 union all select 8 union all select 9) st2,
(select 0 union all select 1 union all select 3 union all select 4 ) st3,
(SELECT #row:=1420070400) st00
) S
left outer join T
on T.date BETWEEN S.r0 AND S.r1
where r1 <= 1451520000