Difference between two fields at different time

[Marvin]

Hi ,

I've got that

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Table : valeur

idpoints horodatage valeur

3 | 01-07-2010 00:00:00 | 451

3 | 01-07-2010 00:05:00 | 451

3 | 01-07-2010 00:10:00 | 451

...

3 | 31-07-2010 23:45:00 | 1000

3 | 31-07-2010 23:50:00 | 1000

3 | 31-07-2010 23:55:00 | 1000

*******************************************************

Table : Consoparpoints

idpoints mensuelle

3

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The aim is to get the difference between the last value of the month and the first one ( ex : 1000 - 451 ) and to put it in consoparpoints.mensuelle

I don't know how to do it, if anyone have an idea I'll take it

Thanks for your help

[comment]

Please update your profile to reflect your version.

Do you need this for display only, or are you going to do anything further with the result?

the last value of the month

How do you determine which month (assuming there are more records in the Values table)?