Aggregate values based on a date interval - mysql

Question

I have a database containing monthly precipitation values at some measurements locations. The structure of my table is:
describe pp_lunare;
Field Type Null
ID int(11) NO
DATA_OBS date NO
PLUTON float NO
LEGHIN float NO
DUMBRAVA float NO
A sample of my data:
ID DATA_OBS PLUTON LEGHIN DUMBRAVA
1 1977-01-01 14.4 33.3 25.1
2 1977-02-01 18.7 12.9 13.2
3 1977-03-01 32.8 26.7 18.3
4 1977-04-01 109.6 123.8 140.6
5 1977-05-01 98.5 104.7 59.9
6 1977-06-01 192.9 172.8 66.6
7 1977-07-01 101.4 85.8 79.4
8 1977-08-01 116.4 103.3 105.7
9 1977-09-01 54.5 47.4 51.8
10 1977-10-01 23.6 15.6 11
11 1977-11-01 59.7 44.3 29.7
12 1977-12-01 28.7 13.1 10
In my case I need to get the sum of the precipitation for every column at every 3 months something like this:
ID DATA_OBS PLUTON LEGHIN DUMBRAVA
1 1977-03-01 65.9 72.9 56.6
2 1977-06-01 401 401.3 267.1
3 1977-09-01 272.3 236.5 247.9
and so on...
Thanks.

Answer 1

You can get the month from your date with month(data_obs) which returns a month from 1 to 12. Convert this to a value for the quarter by doing something like floor((month(data_obs) - 1)/3) as quarter to get quarters from 0 to 3.
For example, select data_obs, concat(year(data_obs), floor((month(data_obs) - 1)/3)) as quarter from pp_lunare; should show you both the original date and the derived quarter side by side.
Then group by this new value and sum the rest:
select concat(year(data_obs), floor((month(data_obs) - 1)/3)) as quarter, sum(pluton), sum(leghin), sum(dumbrava)
from pp_lunare
group by quarter
order by quarter;
If you want the exact date format you had in the question, you'll have to do a little bit of string manipulation (add 1 to the quarter above, multiply that by 3, pad with 0s, then tack on a "-01" for the date).

Answer 2

You can get the month data at first, and convert it into [quarter], which is from 0 to 2.
Then you can create three temporary tables given [quarter]=0,1,2,
and the easy and final part will be to add up the i_th row in these tables, the result will be just like below. And you can also have the data_obs data as well.
ID DATA_OBS PLUTON LEGHIN DUMBRAVA
1 1977-03-01 65.9 72.9 56.6
2 1977-06-01 401 401.3 267.1
3 1977-09-01 272.3 236.5 247.9