Removing where building data is null in CartoDB?

Question

I am new to GIS systems and am beginning with CartoDB. I have extracted polygon data from Open Street Map which I have uploaded and added as a dataset. The data shows building footprints but these seem to disappear into another poloygon(?) which shows the broader site boundaries; in essence everything is highlighted bar the roads when what I actually want is only the building footprints highlighted.

Anyway, in the table I have a lot of rows where the value in the building column is null. When I use the filter to switch this off, I achieve what i need. However, this is only possible when viewing the list layout (I just switch off null) because for city size data it says too much data to view as a list so I have to search to filter if that makes sense and I'm not sure how to switch it off this way?

I have also tried a basic SQL query on the table which did not seem to work:

SELECT * FROM map_table;
DELETE FROM map_table WHERE building = "null";

I'm new to programming so probably making some basic errors but if someone could shed some light or point me in the right direction?

Answer 1

There are two basic ways to achieve what you're trying to do. The first is using the filters like you already tried. This filters out the data by producing a SQL query in the SQL tray and then running it against your data set. It should look something like this:

SELECT * FROM map_table WHERE building is null

It's perfectly acceptable to keep this query there while building your map.

If you want to delete that data from your dataset, first make a copy of your data.

Next, you can run the following query against your table to delete the buildings:

DELETE FROM map_table WHERE building is null

This will remove the rows from your data table permanently--there's no undo button with this operation.

You can checkout some more on the basics of SQL and PostGIS, the querying languages behind CartoDB's data mapping, at CartoDB's Map Academy. There are a couple of lessons on SQL/PostGIS.