QGIS - Using Rule Based Labels With Related Tables

Question

I have a two csv tables that have been related to eachother (RelatedResults):

Table 1 = Locations which is loaded as points Which has the fields[ID] [Type] [X] [Y]

Example: Point_1, Frogs, LAT, LONG

Table 2 = Results which is loaded as just an attribute table Which has the fields [ID] [Year] [ResultA] [ResultB]

Example:

Point_1, 2017, 2000, 4000

Point_1, 2018, 6000,150

I am trying to label the points based upon the year of sampling and every time I try to do it will only label using the result from 2017.

I have tried:

Filter

relation_aggregate( 'RelatedResults', 'count', CASE WHEN "Year" = '2018' THEN 'true' ELSE Null END )

Label Expression Generator

attribute(get_feature('Results', 'ID', ID), 'ResultA')

Not sure what I am doing incorrectly to get this to work as it will only ever show "2000" from the first year of results.

Any help would be amazing guys :). I have been stuck on this for a couple of days now. I need to produce concentration contours across a large areas for each year going back to 1985...

• Jakob: You can probably do it your way, but why no be free as a bird and use sql in a virtual layer: select t1.x,t1.y, t1.geometry, t2.year from table1 t1 inner join table2 t2 using (id). Assuming you have geometry in table1. BTW x is long not lat.
• LeadStar: @Jakob. Thanks for that, I am not too great at SQL to write the inner join expression. Would I be able to have a hand with it? Thanks again!
• LeadStar: @Jakob sorry I spoke too soon! Thank you so much for your help! I now just have to wrangle with the contouring addin. Thank you again

Answer 1

You can probably do it your way, but why not be free as a bird and use sql in a virtual layer:

select t1.x,t1.y, t1.geometry, t2.year 
from table1 t1 
inner join table2 t2 using (id)

Assuming you have geometry in table1. BTW x is long not lat.

A lot of data stuff in QGIS an be handled with a virtual layer. A lot easier to remember than where a dialog with 10 mouse clicks in it is hidden ...