sum up graphs from different streams but slightly different timestamps - postgresql

Question

Right now I try to solve a problem which seems for my understanding somehow related to Finding gaps in huge event streams?
I have several streams of data in my table. I want to sum them up by time, but they have not always the same timestamp. The table looks like this:
Schema:
CREATE TABLE Table1
("id" int, "stream_id" int, "timestamp" timestamp, "value" real)
;
INSERT INTO Table1
("id", "stream_id", "timestamp", "value")
VALUES
(1, 7, '2015-06-01 15:20:30', 0.1),
(2, 7, '2015-06-01 15:20:31', 0.2),
(3, 7, '2015-06-01 15:20:32', 0.3),
(4, 7, '2015-06-01 15:25:30', 0.5),
(5, 7, '2015-06-01 15:25:31', 1.0),
(6, 6, '2015-06-01 15:20:31', 1.1),
(7, 6, '2015-06-01 15:20:32', 1.2),
(8, 6, '2015-06-01 15:20:33', 1.3),
(9, 6, '2015-06-01 15:25:31', 1.5),
(10, 6, '2015-06-01 15:25:32', 2.0)
;
My attempt to solve it:
with ts as (select "timestamp"
from Table1
order by "timestamp"
),
data as (select "timestamp","value"
from Table1
order by "timestamp"
),
streams as (select "stream_id"
from Table1
group by "stream_id"
order by "stream_id"
)
select * .... (question)
I wish to get a graph line for all summed up data. When at a time, there is no data in the other streams, the sum should take the line, which timestamp < current_timestamp but nearest at the current time_stamp. If there is no value, assume 0.
I thought about recursive queries, but I somehow don't see the solution...
EDIT: Here I tried to explain it graphically:
EDIT 2:
I think about something like this, but I don't get the last "thingy" to finish it.
with RECURSIVE data as (
select * from rawdata
where date(date_time)='2014-05-01'
),
streams as (
select stream_id from data
group by stream_id
),
t(n) AS (
VALUES (1)
UNION ALL
SELECT n+1 FROM t WHERE n < (select count(*) from streams)
)
SELECT n FROM t;

Answer 1

I apologize, there was an error in the previous query
Here is a new, corrected query:
WITH times AS(
SELECT DISTINCT "timestamp" As tm
FROM table1
)
SELECT tm, SUM( val ) as s_u_m
FROM (
SELECT tm, "stream_id",
( SELECT "value" FROM Table1 t2
WHERE t2."timestamp" = max( t1."timestamp" )
AND t2."stream_id" = t1."stream_id"
ORDER BY "id" DESC LIMIT 1
) As val
FROM times t
JOIN table1 t1
ON t.tm >= t1."timestamp"
GROUP BY tm, "stream_id"
order by tm
) you_must_have_an_alias_here_in_order_to_avoid_the_syntax_error
GROUP BY tm
ORDER BY tm;
;
and a demo with 3 streams in the source data: http://sqlfiddle.com/#!15/30eb8/5
This is a source table with a layout that mimics the layout of your graph:
| x | id | timestamp | stream6 | stream7 | stream8 |
|----|----|------------------------|---------|---------|---------|
| 1 | 1 | June, 01 2015 15:20:30 | (null) | 0.1 | (null) |
| 2 | 2 | June, 01 2015 15:20:31 | (null) | 0.2 | (null) |
| 3 | 3 | June, 01 2015 15:20:31 | 1.1 | (null) | (null) |
| 4 | 4 | June, 01 2015 15:20:32 | (null) | 0.3 | (null) |
| 5 | 5 | June, 01 2015 15:20:32 | 1.2 | (null) | (null) |
| 6 | 11 | June, 01 2015 15:20:32 | (null) | (null) | 2.3 |
| 7 | 12 | June, 01 2015 15:20:32 | (null) | (null) | 1.1 |
| 8 | 10 | June, 01 2015 15:20:33 | 1.3 | (null) | (null) |
| 9 | 13 | June, 01 2015 15:20:33 | (null) | (null) | 1.7 |
| 10 | 6 | June, 01 2015 15:25:30 | (null) | 0.5 | (null) |
| 11 | 7 | June, 01 2015 15:25:31 | 1.5 | (null) | (null) |
| 12 | 8 | June, 01 2015 15:25:31 | (null) | 1 | (null) |
| 13 | 9 | June, 01 2015 15:25:32 | 2 | (null) | (null) |
And the result is: ( v(3) means: value from a record with x=3)
| tm | s_u_m |
|------------------------|-----------|
| June, 01 2015 15:20:30 | 0.1 | 0 + v(1) + 0
| June, 01 2015 15:20:31 | 1.3000001 | v(3) + v(2) + 0
| June, 01 2015 15:20:32 | 2.6 | v(5) + v(4) + v(7) => see note below !!!
| June, 01 2015 15:20:33 | 3.3 | v(8) + v(4) + v(9)
| June, 01 2015 15:25:30 | 3.5 | v(8) + v(10)+ v(9)
| June, 01 2015 15:25:31 | 4.2 | v(11)+ v(12)+ v(9)
| June, 01 2015 15:25:32 | 4.7 | v(13)+ v(12)+ v(9)
Note for a record | June, 01 2015 15:20:32 | 2.6 |
The source table in the demo contains two records with the same date and the same source_id:
| 6 | 11 | June, 01 2015 15:20:32 | (null) | (null) | 2.3 |
| 7 | 12 | June, 01 2015 15:20:32 | (null) | (null) | 1.1 |
The query picks up only the latest record x=7 due to ORDER BY "id" DESC in this code fragment:
( SELECT "value" FROM Table1 t2
WHERE t2."timestamp" = max( t1."timestamp" )
AND t2."stream_id" = t1."stream_id"
ORDER BY "id" DESC LIMIT 1
) As val
If you want to pick up the first record x=6 instead of the latest, then remove DESC from the order by clause.
If you want to sum all records with the same date and stream_id (in the above example - records 6 + 7), then change the above query to:
( SELECT SUM("value") FROM Table1 t2
WHERE t2."timestamp" = max( t1."timestamp" )
AND t2."stream_id" = t1."stream_id"
) As val
And if you want to pick up a random record, then use ORDER BY random().