How to create a table that loops over data in Postgres - sql

Question

I want to create a table that returns the top 10 aggregate cons_name over a given week, that repeats every day.
So for 5/29/2019 it will pull the top 10 cons_name by their sum dating back to 5/22/2019.
Then, for 5/28/2019, the top 10 cons_name by their sum back to 5/21/2019.
A table of top 10 dating back 7 days all the way to 2018-12-01.
I can make the simple code dating back 7 days but, I have tried Windows to no avail.
SELECT cons_name,
pricedate,
sum(shadow)
FROM spp.rtbinds
WHERE pricedate >= current_date - 7
GROUP BY cons_name, shadow, pricedate
ORDER BY shadow asc
LIMIT 10
This query generates the output below
cons_name pricedate sum
"TEMP17_24078" "2019-05-28 00:00:00" "-1473.29723333333"
"TEMP17_24078" "2019-05-28 00:00:00" "-1383.56638333333"
"TMP175_24736" "2019-05-23 00:00:00" "-1378.40504166667"
"TMP159_24149" "2019-05-23 00:00:00" "-1328.847675"
"TMP397_24836" "2019-05-23 00:00:00" "-1221.19560833333"
"TEMP17_24078" "2019-05-28 00:00:00" "-1214.9914"
"TMP175_24736" "2019-05-23 00:00:00" "-1123.83254166667"
"TEMP72_22893" "2019-05-29 00:00:00" "-1105.93840833333"
"TMP164_23704" "2019-05-24 00:00:00" "-1053.051375"
"TMP175_24736" "2019-05-27 00:00:00" "-1043.52104166667"
I would like a table and function that returns a table of each day's top 10 dating back a week.

Answer 1

Using window functions get's you on the right track but you should be reading further in the documentation about the possibilities.
We have multiple issues here that we need to solve:
gaps in the data (missing pricedate) not get us the correct number of rows (7) to calculate the overall sum
for the calculation itself we need all data rows so the WHERE clause cannot be used to limit only to the visible days
in order to select the top-10 for each day, we have to generate a row number per partition because the LIMIT clause cannot be applied per group
This is why I came up with the following CTE's:
CTE days: generate the gap-less date series and mark visible days
CTE daily: LEFT JOIN the data to the generated days and produce daily sums (and handle NULL entries)
CTE calc: produce the cumulative sums
CTE numbered: produce row numbers reset each day
select the actual visible rows and limit them to max. 10 per day
So for a specific week (2019-05-26 - 2019-06-01), the query will look like the following:
WITH
days (c_day, c_visible, c_lookback) as (
SELECT gen::date, (CASE WHEN gen::date < '2019-05-26' THEN false ELSE true END), gen::date - 6
FROM generate_series('2019-05-26'::date - 6, '2019-06-01'::date, '1 day'::interval) AS gen
),
daily (cons_name, pricedate, shadow_sum) AS (
SELECT
r.cons_name,
r.pricedate::date,
coalesce(sum(r.shadow), 0)
FROM days
LEFT JOIN spp.rtbinds AS r ON (r.pricedate::date = days.c_day)
GROUP BY 1, 2
),
calc (cons_name, pricedate, shadow_sum) AS (
SELECT
cons_name,
pricedate,
sum(shadow_sum) OVER (PARTITION BY cons_name ORDER BY pricedate ROWS BETWEEN 6 PRECEDING AND CURRENT ROW)
FROM daily
),
numbered (cons_name, pricedate, shadow_sum, position) AS (
SELECT
calc.cons_name,
calc.pricedate,
calc.shadow_sum,
ROW_NUMBER() OVER (PARTITION BY calc.pricedate ORDER BY calc.shadow_sum DESC)
FROM calc
)
SELECT
days.c_lookback,
numbered.cons_name,
numbered.shadow_sum
FROM numbered
INNER JOIN days ON (days.c_day = numbered.pricedate AND days.c_visible)
WHERE numbered.position < 11
ORDER BY numbered.pricedate DESC, numbered.shadow_sum DESC;
Online example with generated test data: https://dbfiddle.uk/?rdbms=postgres_11&fiddle=a83a52e33ffea3783207e6b403bc226a
Example output:
c_lookback | cons_name | shadow_sum
------------+--------------+------------------
2019-05-26 | TMP400_27000 | 4578.04474575352
2019-05-26 | TMP700_25000 | 4366.56857151864
2019-05-26 | TMP200_24000 | 3901.50325547671
2019-05-26 | TMP400_24000 | 3849.39595793188
2019-05-26 | TMP700_28000 | 3763.51693260809
2019-05-26 | TMP600_26000 | 3751.72016620729
2019-05-26 | TMP500_28000 | 3610.75970225036
2019-05-26 | TMP300_26000 | 3598.36888491176
2019-05-26 | TMP600_27000 | 3583.89777677553
2019-05-26 | TMP300_21000 | 3556.60386707587
2019-05-25 | TMP400_27000 | 4687.20302128047
2019-05-25 | TMP200_24000 | 4453.61603102228
2019-05-25 | TMP700_25000 | 4319.10566615313
2019-05-25 | TMP400_24000 | 4039.01832416654
2019-05-25 | TMP600_27000 | 3986.68667223025
2019-05-25 | TMP600_26000 | 3879.92447655788
2019-05-25 | TMP700_28000 | 3632.56970774056
2019-05-25 | TMP800_25000 | 3604.1630071504
2019-05-25 | TMP600_28000 | 3572.50801157858
2019-05-25 | TMP500_27000 | 3536.57885829499
2019-05-24 | TMP400_27000 | 5034.53660146287
2019-05-24 | TMP200_24000 | 4646.08844632655
2019-05-24 | TMP600_26000 | 4377.5741555281
2019-05-24 | TMP700_25000 | 4321.11906399066
2019-05-24 | TMP400_24000 | 4071.37184911687
2019-05-24 | TMP600_25000 | 3795.00857752701
2019-05-24 | TMP700_26000 | 3518.6449117614
2019-05-24 | TMP600_24000 | 3368.15348120732
2019-05-24 | TMP200_25000 | 3305.84444172308
2019-05-24 | TMP500_28000 | 3162.57388606668
2019-05-23 | TMP400_27000 | 4057.08620966971
2019-05-23 | TMP700_26000 | 4024.11812392669
...