coordinate system - Changing SRID of existing data in PostGIS?

While importing my shapefile data to PostGIS, I did not select the proper Projection.

How do I now change the SRID of the data, without transforming the Coordinates?

Answer

There is a single line function which does this for you. Just use the following SQL query:

select UpdateGeometrySRID('Schema Name', 'mytable', 'the_geom', newSRID) ;

But, if you are like me, you would be interested in the low level, miniature steps. Logically speaking, the above function is equivalent to the following four step process:

1. 
   

   In the geometry_columns table, update the SRID to the required value.

   
   


2. 
   

   Drop the contraint on the table, by using the following SQL statement

   
   
   

   ALTER TABLE mytable DROP CONSTRAINT enforce_srid_the_geom;

   
   


3. 
   

   Update the SRID'd of the geometry by using the following SQL statement

   
   

   UPDATE mytable SET the_geom = ST_SetSRID(the_geom, newSRID);

   
   


4. 
   

   Add the contraint back by using the following SQL statement

   
   

   ALTER TABLE mytable

   
   

   ADD CONSTRAINT enforce_srid_the_geom CHECK (st_srid(the_geom) = (newSRID));