mysql - Finding changes in value by dates -

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i have table this:

datetime               |  value ----------------------------------- 2015-05-01 12:23:41    |  12  2015-05-01 22:13:11    |  21  2015-05-02 9:13:41     |  23  2015-05-02 17:23:41    |  32

each day has 100 entries @ random time. need calculate following:

  1. daily increase - difference between first entry of today , first entry of yesterday (for each day)
  2. daily avg increase - difference between avg value today , avg value yesterday (for each day)

how can write sql query these values?

what first entry of each date group date portion, , minimum datetime this:

select date(datecol), min(datecol) mytable group date(datecol);

this see results like:

| 2015-05-01 | 2015-05-01 12:23:41 |

once have values, can join 2 tables each date next previous one, this:

select t1.firstdate, t2.seconddate from(   select date(datecol) wholedate, min(datecol) firstdate   mytable   group date(datecol)) t1 join(   select date(datecol) wholedate, min(datecol) seconddate   mytable   group date(datecol)) t2 on t1.wholedate < t2.wholedate , t2.wholedate = (select min(date(datecol)) mytable date(datecol) > date(t1.wholedate));

then, have adjust select statement difference. have join original table values:

select t1.firstdate, t2.seconddate, (s.value - f.value) difference from(   select date(datecol) wholedate, min(datecol) firstdate   mytable   group date(datecol)) t1 join(   select date(datecol) wholedate, min(datecol) seconddate   mytable   group date(datecol)) t2 on t1.wholedate < t2.wholedate , t2.wholedate = (select min(date(datecol)) mytable date(datecol) > date(t1.wholedate)) join mytable f on f.datecol = t1.firstdate join mytable s on s.datecol = t2.seconddate;

for second part, you'll need calculate average each date, , join tables in similar way see difference of averages date date.

here sql fiddle example, , here similar question might well.


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