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I have one source shapefile like this: It consist the geographical coordinates of weather stations:

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And several attribute files, which contain the Temperature data of each date for several years

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I managed to linked them through the ID (project properties/ Relations).

Now I want to access for example the Temperature from the weather station 3 at a specific date. With the attribute table I can see all the values, but I don't know how to query some values with the Field Calculator. I can’t access the linked data.

marked as duplicate by underdark qgis May 20 '17 at 13:27

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    Haven't really used Project Relations so I would probably suggest Joining the shapefile to your attribute files instead. You can do this by accessing your source layer properties (right-click your layer) and (assuming your German) select Eigenshaften > Verknüpfungen, add the attribute files and select the ID fields to join with the relevant field from the source layer. Once done, open the Attribute Table for your source layer, click the bottom-left button and select Fortgeschrittener Filter and use an expression like "ID" = 3 AND "Date" = '2014-01-01'. – Joseph May 18 '16 at 9:58
  • "I dont know how to query some values with the Field Calculator" - can you elaborate on this? What exactly are you trying to achieve? (eg get the count of related features? or the sum of some attribute of related features?) – ndawson May 18 '16 at 22:10
  • Thank for you your response. Now I want to access for example the Temperature from the weather station 3 at a specific date, but i want to use the field calculator of the source attribute table – Hans Vader May 19 '16 at 11:20