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Asked: 2026-06-15T16:00:54+00:00

I am trying to get logging data from a table. Where I select a

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I am trying to get logging data from a table. Where I select a timespan (“maandag” till “vrijdag”). This gets the results I want but now I get the question to only show 3 measurements per day.

The first one being the first after 8 o clock
The second one being the first one after 14:00 o closk
and the third the first one after 20:00 o clock

The problem I have is that the time of the measurements is not constant. So using a regexp to select a part of the day doesn’t work.
With the query below I sometimes also get 2 or 4 or even more results per day. This is because basicly the time between measurements is 2 hours but this is not constant neither is it so that measurements the next day are on the same time.

Is it possible to group by a part of the day?
Or what other solution is there?

data:
id datumTijd ph tbc temperatuur vbc gbc
1 2012-10-03 14:59:19 7.30.08 24.91 0.02 0     
1 2012-10-03 16:47:38 7.33.07 22.15 0.12 0
3 2012-10-03 17:03:06 7.31.09 23.23 0.05 0


query:
SELECT N.name, D.datumTijd, ROUND(D.gbc,2), ROUND(D.vbc,2), ROUND(D.tbc,2),ROUND(D.ph,2), ROUND(D.temperatuur,1)  
FROM METING.Name N, METING.Data D 
Where D.datumTijd BETWEEN "'+maandag+' 00:00:00" AND "'+vrijdag+' 23:59:59"  
AND N.id = D.id AND D.datumTijd 
AND D.datumTijd REGEXP "0[78]:..:..|1[34]:..:..|2[12]:..:.."';
ORDER BY N.name, D.datumTijd
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1 Answer

  1. Editorial Team

    You could do something like this to group results into the 3 different periods. You could then use aggregate functions (SUM, MIN, MAX) on your measures.

    SELECT   DATE(D.datumTijd),
         CASE WHEN TIME(D.datumTijd) BETWEEN '08:00:00' AND '14:00:00' THEN 1
              WHEN TIME(D.datumTijd) BETWEEN '14:00:00' AND '20:00:00' THEN 2
              WHEN TIME(D.datumTijd) BETWEEN '20:00:00' AND '24:00:00' THEN 3
         END as period
...
GROUP BY DATE(D.datumTijd),
         CASE WHEN TIME(D.datumTijd) BETWEEN '08:00:00' AND '14:00:00' THEN 1
              WHEN TIME(D.datumTijd) BETWEEN '14:00:00' AND '20:00:00' THEN 2
              WHEN TIME(D.datumTijd) BETWEEN '20:00:00' AND '24:00:00' THEN 3
         END
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