Problems building a graph using sql SUM

Question

Hello !
i'm curently having issues to build a particular graph :
First, i have a database (moves) which contains 2 columns (timestamp DATETIME, dist NUMERIC), i have no problems to display a graph with these values (even using a time range such 'now','-1 hours', etc.).
But i'd like to build a graph with for example a 2 hours range which gonna display the sum of the value 'dist' every 30 seconds. So for example, if i have 2 'dist' values (3 and 4) at 0min 30sec, the graph will display 7 and the next value will be the sum of
the next 30 secondes dist values.
I tried this :
curs.execute("SELECT timestamp,SUM(dist) AS dist30 FROM moves WHERE timestamp>datetime('now','-30secondes')"
curs.execute("SELECT timestamp,dist30 FROM moves WHERE timestamp>datetime('now','-1 hours')"
But it looks like the column dist30 is not created, and i think this is not gonna work if i want to change the 1 hour range...
I would like a better "algorythme", the table is filled in an other program, should i directly create a 3  columns table and SUM the dist in dist30 directly ?
Thanks for your advice !

Answer 1

Hi Subby,
Regarding your description, are you trying to rollup the dist column by every 30 seconds in a given 2 hours range? If my understanding I correct, you may reference the below sample. As you didn't post any detail about your function datetime(after the where
clause), so the sample is just in a usual way.
CREATE TABLE moves(timestamp DATETIME, dist NUMERIC)
INSERT INTO moves VALUES('2015-02-13 14:20:01',1)
INSERT INTO moves VALUES('2015-02-13 14:20:17',2)
INSERT INTO moves VALUES('2015-02-13 14:20:29',5)
INSERT INTO moves VALUES('2015-02-13 14:22:37',2)
INSERT INTO moves VALUES('2015-02-13 14:22:56',5)
INSERT INTO moves VALUES('2015-02-13 14:27:17',2)
SELECT timestamp,SUM(dist) AS dist30 FROM(
SELECT DATEADD(SECOND,DATEPART(SECOND,timestamp)%30*-1,timestamp) AS timestamp,dist FROM moves) AS T --rollup by every 30 seconds
WHERE timestamp BETWEEN '2015-02-13 13:00:00' AND '2015-02-13 15:00:00' --two hour range
GROUP BY timestamp
If you have any question, feel free to let me know.
Eric Zhang
TechNet Community Support