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-- script de calcul des distances sources
set search_path to rht,public;
select cast(ltree2text(subltree(chemin,0,1)) as integer) from rht_topology limit 10
/*
AJOUT D'UN INDEX
ltree supports several types of indexes that can speed up the indicated operators:
    B-tree index over ltree: <, <=, =, >=, >
    GiST index over ltree: <, <=, =, >=, >, @>, <@, @, ~, ? 
*/
CREATE INDEX chemin_btee_index ON rht.rht_topology USING btree(chemin); --27688 ms
VACUUM ANALYSE rht.rht_topology;
CREATE INDEX chemin_gist_index ON rht.rht_topology USING GIST (chemin); -- fait planter mon serveur....
SELECT * from rht.rht_topology where chemin <@ '212340'; -- tronçon source de la Vilaine -- 2360
SELECT chemin from rht.rht_topology where chemin <@ '212340' limit 1
-- La distance source est la distance mer maximale de tous les chemins possibles en ne prenant que le dernier tronçon du chemin.
Select max(dmer) from rht.rht_topology where id_drain in (
Select cast(ltree2text(subpath(chemin, -1, 1))as integer) as chenin_id_drain from rht.rht_topology where chemin <@ '212340');

--  fonction pour renvoyer les distances source
DROP FUNCTION IF EXISTS rht.distance_source();
CREATE OR REPLACE FUNCTION rht.distance_source() RETURNS integer AS $$
DECLARE
    id_drains RECORD;
    nbligne integer;
BEGIN
          nbligne:=1;
          DROP TABLE IF EXISTS rht.distance_mer;
          CREATE TABLE rht.distance_mer (id_drain integer,distance_mer  numeric);
          FOR id_drains IN SELECT id_drain FROM rht.rht_topology ORDER BY id_drain LOOP
                  -- pour vérification décommenter ensuite
                  RAISE NOTICE 'distance_source for %', quote_ident(CAST(id_drains.id_drain as text));
                  EXECUTE 'INSERT INTO rht.distance_mer SELECT MAX(dmer) FROM rht.rht_topology WHERE id_drain IN (
                        SELECT CAST(ltree2text(subpath(chemin, -1, 1))as integer) FROM rht.rht_topology where chemin <@  text2ltree(cast ('||
                        id_drains.id_drain
                        || 'as text)) )';  
                nbligne=nbligne+1;      
        END LOOP;
    RETURN nbligne;
END;
$$ LANGUAGE plpgsql;

select rht.distance_source();

utilisation des donnees de parcours

En pratique nous n'aurons probablement besoin que du noeud le plus amont des parcours comme programmé ci dessus. Mais les scripts ci-dessous pourraient s'avérer utiles.
Ci dessous la fonction utilise les expressions régulières ltree => vecteur => table

/*
regexp_split_to_array(string text, pattern text [, flags text ]) 	regexp_split_to_array('hello world', E'\\s+')	{hello,world}
SELECT regexp_split_to_array('hello world', E'\\s+');
SELECT regexp_split_to_array('hello.world', E'\\.+');
*/
SELECT regexp_split_to_array(ltree2text(chemin),E'\\.+') from rht.rht_topology where chemin <@ '212340';

/*
http://www.pgsql.cz/index.php/PostgreSQL_SQL_Tricks#Array_to_table
SELECT (ARRAY[1,3,4,6,7])[idx.n] FROM generate_series(1,7) idx(n);
CREATE OR REPLACE FUNCTION unpack(anyarray)
RETURNS SETOF anyelement AS $$ 
SELECT $1[i] 
   FROM generate_series(array_lower($1,1), 
                        array_upper($1,1)) g(i);
$$ LANGUAGE sql STRICT IMMUTABLE;
*/
CREATE OR REPLACE FUNCTION unpack(anyarray)
RETURNS SETOF anyelement AS $$ 
SELECT $1[i] 
   FROM generate_series(array_lower($1,1), 
                        array_upper($1,1)) g(i);
$$ LANGUAGE sql STRICT IMMUTABLE;
-- pour convertir un vecteur en table
select unpack(vecteurchemin) from 
	(SELECT regexp_split_to_array(ltree2text(chemin),E'\\.+') as vecteurchemin from rht.rht_topology where chemin <@ '212340' limit 1) as sub
-- j'avais pas vu il y a déjà une fonction magique unest...
select cast(unnest(vecteurchemin) as integer) as chemin_id_drain from
	(SELECT regexp_split_to_array(ltree2text(chemin),E'\\.+') as vecteurchemin from rht.rht_topology where chemin <@ '212340' limit 1) as sub
-- Fonction qui renvoit les identifiants uniques des tronçons en amont d'un ouvrage


CREATE OR REPLACE FUNCTION troncons(integer)
RETURNS SETOF integer AS $$
select cast(unnest(vecteurchemin) as integer) as chemin_id_drain from
	(SELECT regexp_split_to_array(ltree2text(chemin),E'\\.+') as vecteurchemin from rht.rht_topology where chemin <@ text2ltree(cast ($1 as text))  limit 1) as sub;
$$ LANGUAGE sql STRICT IMMUTABLE;	

SELECT troncons_amont(212340); -- OK