Find_SRID — Returns the SRID defined for a geometry column.
integer Find_SRID(varchar a_schema_name, varchar a_table_name, varchar a_geomfield_name);
Returns the integer SRID of the specified geometry column by searching through the GEOMETRY_COLUMNS table. If the geometry column has not been properly added (e.g. with the AddGeometryColumn function), this function will not work.
SELECT Find_SRID('public', 'tiger_us_state_2007', 'geom_4269');
find_srid
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4269