PostGIS, create centroid column from polygon column

Question

I have a table like this:

id|      shape [geometry]     |  centroid [geomety]
---------------------------------------------------
 1|MULTIPOLYGON(((-70, etc...)|
 2|MULTIPOLYGON(((-71, etc...)|

I need to create the centroid of each shape, how can I do this? The final result should be this table:

id|      shape [geometry]     |  centroid [geomety]
---------------------------------------------------
 1|MULTIPOLYGON(((-70, etc...)|POINT(something)
 2|MULTIPOLYGON(((-71, etc...)|POINT(something_else)

Edit: should be some update with st_centroid(shape) I guess

Answer 1

ALTER TABLE my_table ADD COLUMN centroid GEOMETRY;
UPDATE my_table SET centroid = ST_Centroid(geom);

If you need to be certain that the point is within the polygon however, use ST_PointOnSurface():

ALTER TABLE my_table ADD COLUMN centroid GEOMETRY;
UPDATE my_table SET centroid = ST_PointOnSurface(geom);

Further reading:

• ST_Centroid()
• ST_PointOnSurface()