How to represent distances between two coordinates - cartodb

Question

I have a simple DataSet with 2 different coordinates by record.
(dem_latitude & dem_longitude are one coordinate, html_latitude & html_longitude are the other coordinate)
My main purpose is to see how big are the distances between each couple of coordinates.
As an clarification I don't want to see the distance as a number but represented in the map with the 2 coordinates (that form a couple) easily recognisable.
Solutions I can image but I don't know how to develop:
I can see for each coordinate which is its partner, maybe through a line.
Events like clicking in one coordinate makes the partner coordinate to be highlighted.
Any suggestion of how to implement any of this solutions or any other suggestion to achieve my "main purpose"?
If the solution is using the WYSIWYG CartoDB editor better :)

Answer 1

CartoDB UI and CartoDB WYSIWYG are very good and intuitive but when working with a single geometry per row. I'm not an expert, but I think in this case you'll need to use your developer super-powers and:
1 - alter the table schema and add a new column distance
2 - run a simple query to update that column value based on the points information:
UPDATE <table_name> SET distance = (SELECT ST_Distance(
ST_GeographyFromText(
'SRID=4326;POINT(' || dem_longitude || ' ' || dem_latitude || ')'
),
ST_GeographyFromText(
'SRID=4326;POINT(' || html_longitude || ' ' || html_latitude || ')'
)
)
);
Remember you can run queries using the API, so it's easy to integrate this query in any callback that adds data to the table to keep it updated.

Answer 2

Inspired by the #blat's answer, and after dealing with a lot of weird errors with SRIDs codes and the_geom_webmercator vs the_geom, I got this solution:
select
st_transform(
st_makeline(
st_setsrid(st_makepoint(html_longitude,html_latitude), 4326),
st_setsrid(st_makepoint(dem_longitude,dem_latitude), 4326)
),
3857
) as the_geom_webmercator
from the_data_set
If you also want to show the initial and the end point you have to create extra layers for each coordinate couple and then do something like:
select
cartodb_id,
st_transform(
st_setsrid(st_makepoint(dem_longitude,dem_latitude), 4326),
3857
) as the_geom_webmercator
from the_data_set
The result looks like this: