How to change SRID of geometry column?

Question

I have table where the one of columns is geometry column the_geom for polygons with SRID. I added new column in the same table with exactly the same geometry data as in the_geom. This another column has name the_geom4258 because I want here to set up another SRID=4258. So what is the procedure to set up another SRID geometry to be changed (in another coord.system)? Is just enough to apply following query:

UPDATE table SET the_geom4258=ST_SetSRID(the_geom4258,4258);

Answer 1

You should use the ST_Transform function. Also use the function AddGeometryColumn to create your new column, to ensure all the necessary constraints are also created:

SELECT AddGeometryColumn('table','the_geom4258',4258, 'POLYGON', 2);

UPDATE table SET the_geom4258 = ST_Transform(the_geom,4258);

ST_SetSRID just sets the projection identifier, but does not actually transform the geometries.