mysql query to identify groups of data based on timestmp - mysql

Question

I have records of smartmeter in an mysql database.
Records in timestamp order looking in generall as follow:
key
timestamp
watt now
000001
2022-10-04-01-01-01
10
000002
2022-10-04-01-02-01
10
000003
2022-10-04-01-03-01
101
000004
2022-10-04-01-04-01
101
000005
2022-10-04-01-05-01
102
000006
2022-10-04-01-06-01
101
000007
2022-10-04-01-07-01
102
000008
2022-10-04-01-08-01
10
000009
2022-10-04-01-09-01
10
000010
2022-10-04-01-09-01
10
000011
2022-10-04-01-09-01
107
000012
2022-10-04-01-09-01
101
000013
2022-10-04-01-09-01
109
000014
2022-10-04-01-09-01
10
000015
2022-10-04-01-09-01
10
I want to identify the groups with bigger number (lets say > 100)
and give them an incresing id. Also I want to get per group the first and last key id
Result of query should look like this:
month
day
numbers of group
first id
last id
average watt
10
04
0
000003
000007
102
10
04
1
000011
0000013
105
Any help apreciated

Answer 1

You'll need something to identify them as a group. My first thought was using RANK() or DENSE_RANK() but after multiple tries, I couldn't find a way. Then I thought about using LAG() but still I'm stuck at how to re-identify the rows as new group. After testing many times, I come up with this suggestion:
WITH cte AS (
SELECT s1.*,
#n := COALESCE(IF(s1.skey=1,1,s2.skey), #n) As newGroup
FROM smartmeter s1
LEFT JOIN (
SELECT skey,
stimestamp,
watt,
LENGTH(watt) AS lenwatt,
LAG(LENGTH(watt)) OVER (ORDER BY skey) llwatt
FROM smartmeter) s2 ON s1.skey=s2.skey
AND lenwatt != llwatt)
SELECT MONTH(stimestamp) AS Month,
DAY(stimestamp) AS Day,
ROW_NUMBER() OVER (ORDER BY MIN(skey)) AS 'numbers of group',
MIN(skey) AS 'first id',
MAX(skey) AS 'last id',
AVG(watt) AS 'Average watt',
CEIL(AVG(watt)) AS 'Average watt rounded',
newGroup
FROM cte
WHERE watt >= 100
GROUP BY newGroup, MONTH(stimestamp), DAY(stimestamp)
By the way, I've changed some of your column names because key is actually a reserve word. Although you can use it as column name as long as you wrap it in backticks, I personally find it's a hassle to do it every time.
Ok, so my idea was to use LENGTH(watt) and ORDER BY skey in the LAG() function. Then I'll separate those rows where the length doesn't match and use that as a starting point for each new group. After that, I left join the result of that with smartmeter table. The next challenge is to assign each of the rows that doesn't match with previous skey value then I've found this answer and applied it into the cte.
Once those are done, I just write another query to fulfil your expected result. Although, some part of it is not exactly as what you expected.
Here's a demo fiddle