How to make projections with future dates using Redshift - sql

Question

I currently have a table called quantities with the following data:
+------+----------+----------+
| item | end_date | quantity |
+------+----------+----------+
| 1 | 26/11/17 | 100 |
+------+----------+----------+
| 2 | 28/11/17 | 300 |
+------+----------+----------+
| 3 | 30/11/17 | 500 |
+------+----------+----------+
I want to query it so I can get this result:
+--------+-------+
| date | total |
+--------+-------+
| 26-Nov | 900 |
+--------+-------+
| 27-Nov | 800 |
+--------+-------+
| 28-Nov | 800 |
+--------+-------+
| 29-Nov | 500 |
+--------+-------+
| 30-Nov | 500 |
+--------+-------+
How would this query look like? Many thanks!
Please note:
The above output is the result of suming the "quantity" field of each item when today's date is =< end_date. See below that today is the 26th of november.
+--------+-----+-----+-----+-------+
| date | 1 | 2 | 3 | total |
+--------+-----+-----+-----+-------+
| 26-Nov | 100 | 300 | 500 | 900 |
+--------+-----+-----+-----+-------+
| 27-Nov | - | 300 | 500 | 800 |
+--------+-----+-----+-----+-------+
| 28-Nov | - | 300 | 500 | 800 |
+--------+-----+-----+-----+-------+
| 29-Nov | - | - | 500 | 500 |
+--------+-----+-----+-----+-------+
| 30-Nov | - | - | 500 | 500 |
+--------+-----+-----+-----+-------+
I'd need the query to always give an output with the following date range:
start_date=current_date
end_date=the latest end_date from the list of items
I am using PostgreSQL 8.0.2 on i686-pc-linux-gnu, compiled by GCC gcc (GCC) 3.4.2 20041017 (Red Hat 3.4.2-6.fc3), Redshift 1.0.1499

Answer 1

t=# create table so (item serial, end_date date, quantity int);
CREATE TABLE
t=# set datestyle TO DMY;
SET
t=# insert into so(end_date,quantity) values('26-11-2017',100),('28-11-2017', 300), ('30-11-2017', 500);
INSERT 0 3
then, we create a view with a date series that goes into the future starting from today by using a table with a sequential id column:
CREATE VIEW future_dates AS
SELECT (getdate()::date -1 + id)::date as future_dates
FROM app_data.table_with_sequential_id
ORDER BY future_dates
N.b. We need to create the above view because generate_series is not fully supported in Redshift.
and lastly select itself:
t=# select gs::date, sum(quantity) over (order by gs desc rows unbounded preceding)
from future_dates gs
left outer join so on so.end_date = gs
order by gs ;
gs | sum
------------+-----
2017-11-26 | 900
2017-11-27 | 800
2017-11-28 | 800
2017-11-29 | 500
2017-11-30 | 500
(5 rows)