PostGIS Cookbook - Second Edition

How to do it...

The first thing we need to do is find all the fields that don't have ampersands and use those as our unique list of available trails. In our case, we can do this, as every trail has at least one segment that is uniquely named and not associated with another trail name. This approach will not work with all datasets, so be careful in understanding your data before applying this approach to that data.

To select the fields ordered without ampersands, we use the following query:

SELECT DISTINCT label_name, res 
  FROM chp02.trails 
  WHERE label_name NOT LIKE '%&%' 
  ORDER BY label_name, res; 

It will return the following output:

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