Question

I have a SQL table with periodic measurements. I’d like to be able to return some summary method (say SUM) over the value column, for an arbitrary number of rows at a time. So if I had

id  |  reading
1      10
5      14
7      10
11     12
13     18
14     16

I could sum over 2 rows at a time, getting (24, 22, 34), or I could sum 3 rows at a time and get (34, 46), if that makes sense. Note that the ID might not be contiguous — I just want to operate by row count, in sort order.

In the real world, the identifier is a timestamp, but I figure that (maybe after applying a unix_timestamp() call) anything that works for the simple case above should be applicable. If it matters, I’m trying to gracefully scale the number of results returned for a plot query — maybe there’s a smarter way to do this? I’d like the solution to be general, and not impose a particular storage mechanism/schema on the data.

Answer 1

You may resequense query result and then group it

SET @seq = 0;

SELECT SUM(data), ts FROM (
    SELECT @seq := @seq + 1 AS seq, data, ts FROM table ORDER BY ts LIMIT 50
) AS tmp GROUP BY floor(tmp.seq / 3);