[Question] Django 2 - how to sum values based on filter and group by Year-Month

[Charles Sartori]

I have the following table:

2018-01-01      10

2018-01-15      20

2018-01-31      30

2018-02-01      10

2018-03-01      10

2018-03-20      20

I need to Sum() the values filtering it with 

1 - sum(values) where date < first day of the month

2 - sum(values) where date < last day of the month

Expected result(something like that):

[

 {'year-month': '2018-01'}, {'sum_before_month_day_one': 0}, {'sum_before_last_month_day': 60},

 {'year-month': '2018-02'}, {'sum_before_month_day_one': 60}, {'sum_before_last_month_day': 70},

 {'year-month': '2018-03'}, {'sum_before_month_day_one': 70}, {'sum_before_last_month_day': 100},

]

So far I manage to sum values and group by month:

In [12]: result = Sale.objects \

    ...:     .annotate(date=TruncMonth('event_date')) \

    ...:     .values('date') \

    ...:     .annotate(quantity=Sum('quantity')) \

    ...:     .values('date', 'quantity') \

    ...:     .order_by('date')

In [13]: for i in result: print(i)

{'date': datetime.date(2018, 1, 1), 'quantity': 60.0}

{'date': datetime.date(2018, 2, 1), 'quantity': 10.0}

{'date': datetime.date(2018, 3, 1), 'quantity': 30.0}

[Gerald Brown]

I am having a similar problem where I want to get the total (SUM) of about 20 - 30 items in a current day.  I can get the list of customers names and payments in a html table but so far haven't been able to get the SUM of those payments.  I have tried using Django ORM AGGREGATE SUM('integer field') but I am not able to get the results. 

I haven't tried grouping yet in my project but will probably have to in the near future.  I think it is possible to group by week & month and then get a sum of those groups.  MariaDB has a function "MONTH" and " WEEKOFYEAR" which I hope will help with the grouping.  One problem that I have is that in my customer table I have a ForeignKey link to a Payment_amount table so the user can look up the payment amount instead of typing it in where an extra/less zero could be entered.

One web site that might offer some suggestions on solving your/my problem is: https://simpleisbetterthancomplex.com/tutorial/2016/12/06/how-to-create-group-by-queries.html.  This site has a lot of posts relating to Django.

Good luck & I would be interested in how you solved this problem.

Gerald S. Brown

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[Melvyn Sopacua]

On vrijdag 27 juli 2018 04:25:56 CEST Charles Sartori wrote:

> I need to Sum() the values filtering it with
> 1 - sum(values) where date < first day of the month
> 2 - sum(values) where date < last day of the month
>
> Expected result(something like that):
> [

> {'year-month': '2018-01'}, {'sum_before_month_day_one': *0*},
> {'sum_before_last_month_day': *60*},
> {'year-month': '2018-02'}, {'sum_before_month_day_one': *60*},
> {'sum_before_last_month_day': *70*},
> {'year-month': '2018-03'}, {'sum_before_month_day_one': *70*},
> {'sum_before_last_month_day': *100*},
> ]

Break it down:
- the only relevant part is the sum of the month
- the other is a running total you can keep track of without putting the
burdon on the database

But, requirement 2) applied to the first result should strictly yield 30, not
60. But I think that's an error in your requirement description.

> {'date': datetime.date(2018, 1, 1), 'quantity': 60.0}

(30 is *at* the last day of the month, not before it)
> 2018-01-31 30

--
Melvyn Sopacua