I have a question about a specific query for a Shapefile-Layer in QGIS 3.4.
I have a Point-Shapefile with the name point.shp. The Shapefile has a lot of different points with a large amount of attributes. But two attributes are interesting for us. The first attribute has the name 'Zone', and the second is called 'Direction'. Both attributes have the data type string.
This picture visualize the structure of the Shape:
Now, we have a rule: in every zone, the direction number must be unique. In the example, all points in zone 9 an 22 are legit. But we have a problem in zone 10. Direction 1 occurs twice. Because of that, all points in zone 10 are invalid.
Can I select all the points, where one zone has multiple directions with identical numbers?
Maybe, when I selected the points with the incorrect rule, I can reverse the selection to export the valid values.