Getting aggregated results by different time intervals - sql

Question

I have a postgres DB with a table containing data according to an id and a timestamp.
The table has several columns with data. I want to create an pgsql function that would allow me to get an aggregation of data according to a time interval.
The table looks something like this:
user_id | created_at | value_a | value_b | value_c | value_d | unique_key
------------+---------------------+---------+---------+---------+---------+------------
1 | 2019-12-16 17:37:07 | 1 | 5 | 0 | 5 | 1
2 | 2019-12-19 15:37:07 | 4 | 7 | 0 | 42 | 2
3 | 2019-12-16 15:37:07 | 20 | 1 | 20 | 143 | 3
2 | 2019-12-18 12:01:32 | 0 | 0 | 5 | 987 | 4
1 | 2019-12-11 14:12:50 | 6 | 0 | 9 | 0 | 5
2 | 2019-12-10 15:37:07 | 1 | 72 | 100 | 90 | 6
1 | 2019-12-20 15:37:07 | 5 | 3 | 56 | 1546 | 7
3 | 2019-12-20 15:37:07 | 30 | 4 | 789 | 3 | 8
4 | 2019-12-01 15:37:07 | 35 | 90 | 0 | 5 | 9
(9 rows)
I want to create the function in a way that I can get a time range (before and after) and an interval so it would then group the data according to the interval (daily for example), group by user_id.
I have managed to create a function with a generate_series that returns the aggregated results, but it ignores some of the data.
The aggregation uses different formulas to get the data.
Most of the answers that I have found managed to select a grouped sum of only one value, and not several, I.E. it returns something along the lines of:
user_id | date | value_a + value_b + value_c + value_c
But in my case I would like to manipulate the data in different ways, for example:
user_id | date | a + b | (a*b)/c | count(a)
etc. (of course I will handle the divide by zero and stuff)..
So the function that I tried to create was something along the lines of:
CREATE OR REPLACE FUNCTION branch_performance_measurements_daily(
IN after DATE,
IN before DATE,
)
RETURNS TABLE (
date_of_sum DATE,
func_a INT,
func_b INT,
func_c INT
)
AS $$
BEGIN
RETURN QUERY
WITH days_series AS (
SELECT d::date day FROM generate_series(after, before, '1 day') day)
SELECT days_series.day AS date_of_sum,
sum(a + b),
sum((a*b)/c),
count(a)
FROM table b
WHERE DATE(b.created_at) = DATE(days_series.day)
GROUP BY days_series.day, b.user_id;
END;
$$ LANGUAGE plpgsql;
Sadly this type of query does not return all the available data in the table according to all dates available..
Is there any way to perhaps point me as to the proper usage of the generate_series for the case that I need?
P.S.
I am aware that the function of the sum won't work, it's just for the example :)
Many thanks in advance!

Answer 1

Welcome to Stack Overflow.
Your functions had a few syntax errors. This is what you might be looking for:
CREATE OR REPLACE FUNCTION branch_performance_measurements_daily(
after DATE, before DATE)
RETURNS TABLE (
date_of_sum DATE, func_a BIGINT,func_b BIGINT, func_c BIGINT) AS $$
BEGIN
RETURN QUERY
WITH days_series AS (
SELECT generate_series(after, before, '1 day') AS d)
SELECT
DATE(ds.d) AS date_of_sum,
sum(value_a + value_b),
COALESCE(sum((value_a*value_b)/NULLIF(value_c,0)),0),
count(value_a) FROM t
JOIN days_series ds ON ds.d = DATE(t.created_at)
GROUP BY ds.d, t.user_id
ORDER BY ds.d;
END;
$$ LANGUAGE plpgsql;
Sample data
CREATE TEMPORARY TABLE t
(user_id INT, created_at date,
value_a int,value_b int,value_c int,value_d int, unique_key int);
INSERT INTO t VALUES
(1,' 2019-12-16 17:37:07',1,5,0,5,1),
(2,' 2019-12-19 15:37:07',4,7,0, 42,2),
(3,' 2019-12-16 15:37:07',20,1,20,143,3),
(2,' 2019-12-18 12:01:32',0,0,5,987,4),
(1,' 2019-12-11 14:12:50',6,0,9,0,5),
(2,' 2019-12-10 15:37:07',1,72,100, 90,6),
(1,' 2019-12-20 15:37:07',5,3,56,1546,7),
(3,' 2019-12-20 15:37:07',30,4,789,3,8),
(4,' 2019-12-01 15:37:07',35, 90,0,5,9);
Testing function
SELECT * FROM branch_performance_measurements_daily('2019-12-01', '2019-12-20');
date_of_sum | func_a | func_b | func_c
-------------+--------+--------+--------
2019-12-01 | 125 | 0 | 1
2019-12-10 | 73 | 0 | 1
2019-12-11 | 6 | 0 | 1
2019-12-16 | 6 | 0 | 1
2019-12-16 | 21 | 1 | 1
2019-12-18 | 0 | 0 | 1
2019-12-19 | 11 | 0 | 1
2019-12-20 | 8 | 0 | 1
2019-12-20 | 34 | 0 | 1
(9 rows)
In case you want to group just by the generated date (not together with the user_id, as your query suggests) just remove the user_id from the GROUP BY clause and you'll get something like this:
date_of_sum | func_a | func_b | func_c
-------------+--------+--------+--------
2019-12-01 | 125 | 0 | 1
2019-12-10 | 73 | 0 | 1
2019-12-11 | 6 | 0 | 1
2019-12-16 | 27 | 1 | 2
2019-12-18 | 0 | 0 | 1
2019-12-19 | 11 | 0 | 1
2019-12-20 | 42 | 0 | 2