How to add a new permanent column that contains result from ST_AREA select queries

Question

I have a bunch of polygons in my CartoDB map, and I want to create a new column called AREA in the table MY_TABLE that contains values from my area calculation query:

select ST_Area(the_geom::geography) as area_sqm FROM My_TABLE

this statement works, but the column area_sqm that contains the area value clears every time I clear the query, how can I have this permanently as part of my table so I can display the area value in the info table of my map?

Answer 1

In general:

ALTER TABLE  your_table ADD COLUMN area double precision;

UPDATE your_table SET area=ST_AREA(geom::geography);

(If your srid is 4326 and your data is stored as geometry)

Edit:

To round to 2 decimals use round() funcrion. If I remember right it works on numeric type and not double precision. So you need something like:

ROUND((ST_Area(geom::geography))::numeric,2)