[GIS] How to label features in QGIS using SQL statement

labelingqgissql

In QGIS, I can't seem to find a way to define the features that I want to label using a SQL query? Is this possible?

For example, I downloaded the OSM Natural shapefiles, and a lot of those features have no values in their "name" field. I would like to display all features, but only label those features where NAME <> "". The same concept could be applied to roads, where TYPE = "Motorway".

In the image below, I want all polygons visible, but don't want to label the 3 polys on the right.

enter image description here

Best Answer

You can now label features using an expression in version 1.8, something like this:

CASE WHEN NOT "NAME" IS NULL THEN "Name" END

CASE WHEN "TYPE" = 'Motorway' THEN "Name" END

Expression labels

Related Solutions

[GIS] Deleting records from multiple, similar feature classes by attribute values using SQL statement in ArcGIS Desktop

One way to automate the processing of this would be with Python by working through a list of the feature classes, and the using an updatecursor/deleteRow statement to delete the unneeded records.

import arcpy

workspace = r"c:\yourworkspace\yourgeodatabase.gdb"  #assuming file geodatabase
arcpy.env.workspace = workspace

#Part 1 -- create list of feature classes in your geodatabase...
#assuming all featureclasses within the geodatabase are of interest for the query -- otherwise specify a wildcard below

featureclasslist = arcpy.ListFeatureClasses()

#now run a loop on feature classes in the list
for featureclass in featureclasslist:


 #Part 2 -- deleting the records specified in your sql query. There are two approaches:

 # option1:
    your_query = " \"yourfield\" = 'your_value' "  #enter your sql query here

    rows = arcpy.UpdateCursor(featureclass, your_query)
    for row in rows:
        rows.deleteRow(row)

    # or option 2

    rows = arcpy.UpdateCursor(featureclass)
    for row in rows:
        if row.getValue("Yourfield") == 'your_value':
            rows.deleteRow(row)

More here on listing featureclasses: http://help.arcgis.com/en/arcgisdesktop/10.0/help/index.html#//000v0000001n000000

and on the updatecursor/deleteRow statement: http://help.arcgis.com/en/arcgisdesktop/10.0/help/index.html#//002z0000001q000000

[GIS] Using “SELECT DISTINCT” in SQL Query for Labels

You can see this answer: Select distinct values from a single column of an attribute table (or layer)
Using Maplex, you can keep labels from repeating within a given distance

Best Answer

Related Solutions

[GIS] Deleting records from multiple, similar feature classes by attribute values using SQL statement in ArcGIS Desktop

[GIS] Using “SELECT DISTINCT” in SQL Query for Labels

Related Question