expressionqgis
I have 2 layers of polygons in QGIS which are layer1 and layer2.
they both have column id.
The goal is to select items in layer1 that not appear in layer2 using unique field id.
For example:
layer 1 has id: 1, 2, 3, 4, 5
layer 2 has id: 1, 2, 3, 4
by using expressions like
id not in layer2
How can I write the expression to have item 5 in layer 1 selected?
As long as the QGIS fix is not ready you can use ogr2ogr for merging the layers. Use it with parameter -unsetFid https://www.gdal.org/ogr2ogr.html. Run this command for all your input layers for appending data from the layers to a single table named "merged"
ogr2ogr -f gpkg -update -append -unsetFid output.gpkg input_layer1 -nln merged
Afterward of @ndawson's comment and @user30184's answer. I wrote a batch file for Windows that iterates in all OUTPUTS with the pattern iterate_*.gpkg and merges all in one file this way:
echo off
set dst_datasource_name=voronoi_merge.gpkg
del %dst_datasource_name%
for %%f in (iterate_*.gpkg) do (
echo Merging %%~nf
ogr2ogr -f gpkg -update -append -unsetFid %dst_datasource_name% %%~nf.gpkg -nln voronoi_merge
)
This file must be run from the folder with all the OUTPUTS
The expression works correctly.
The problem is related to the circle variable which creates a circle for each point.
When we use within (@selected_pt, @circle), QGIS selects all the circles that contain the selected point.
Below a screenshot that demonstrates the above, the selected point is contained only in 5 circles.
Best Answer
You can achieve that using an SQL Query in the DB Manager of QGIS.
You choose Database / Database Manager / Database Manager then Virtual Layers / Qgis Layers you can then try queries like the following :
Depending on the size of your tables it can be a bit time consuming ...