this is ticket: #49 We need to only select a geographical region from the ccm plus all downstream segments within this region.
Below we use the ST_Contains function

/*boolean ST_Contains(geometry geomA, geometry geomB);
Description
Geometry A contains Geometry B 
*/
-- first trial..
/*
SELECT count (*) from ccm21.riversegments r
join (SELECT ST_Union(f.the_geom) as singlegeom
    FROM france.departement As f) as sub
ON ST_Contains(sub.singlegeom,r.the_geom); 
*/
 -- we try to get the vector of seaoutlets that are within the geographical area

-- a table containing three columns

 drop table  if exists france.wso;
 CREATE TABLE france.wso (
 id serial PRIMARY KEY,
 wso_id integer,
 area varchar(12)
 )

insert into france.wso(wso_id) 
select distinct on (wso_id)  wso_id from ccm21.riversegments r
join (SELECT ST_Union(f.the_geom) as singlegeom
    FROM france.departement As f) as sub
ON ST_Contains(sub.singlegeom,r.the_geom); --170703 lines
UPDATE france.wso set area='France' where area IS NULL

select * from ccm21.riversegments where wso_id in (select wso_id from france.wso where area='France')--170703 lines