We used this function in the previous lesson. Recall that we used this function instead of adding the geometry column through the Postgres table definition GUI because PostGIS requires an entry in the geometry_columns view. AddGeometryColumn() handles this for us.
As the name implies, this function does the opposite of AddGeometryColumn().
This function is the equivalent of Esri’s Define Projection tool. Use it if a geometry column has its SRID defined incorrectly. As with the Define Projection tool this function has no effect on coordinate values, it simply modifies the metadata for the geometry column.