如何使用postgis从postgres表中获取连接的线串？

Question

我有一个带有 id、几何形状的表，其中几何形状的类型为线串或多线串。 我想将所有相互连接的线串分组。例如

Id  geometry
 1  linestring(a, b)
 2  linestring(b, c)
 3  linestring(b, d)
 4  linestring(e, f)

那么结果应该是

Id       geometry
1,2,3   linestring(a,b,c,d)
4       linestring(e, f)

我尝试做

st_intersects

和

st_union

，这给出了仅一行的多行字符串。

select STRING_AGG(t.id::TEXT, ', '), st_union(t.geom) from table t
group by ST_intersects(t.geom, t.geom)

Answer 1

一定要喜欢它们的递归 CTE 🥰

WITH RECURSIVE some_points AS (
    SELECT
        ST_MakePoint(0, 0) AS a,
        ST_MakePoint(1, 0) AS b,
        ST_MakePoint(2, 0) AS c,
        ST_MakePoint(1, 1) AS d,
        ST_MakePoint(0, 2) AS e,
        ST_MakePoint(1, 2) AS f
), some_lines AS (
    SELECT
        UNNEST(ARRAY[1,2,3,4]) AS id,
        UNNEST(ARRAY[
            ST_MakeLine(a, b),
            ST_MakeLine(b, c),
            ST_MakeLine(b, d),
            ST_MakeLine(e, f)
        ]) AS geom
    FROM some_points
), paths AS ( -- for each line segment add connected line segments recursively
        SELECT id AS path_id, 1 AS degree, ARRAY[id] AS ids, geom
        FROM some_lines
    UNION ALL
        SELECT p.path_id, degree + 1, ARRAY_APPEND(p.ids, l.id), ST_Union(p.geom, l.geom)
        FROM paths AS p
            INNER JOIN some_lines AS l
                ON ST_Intersects(p.geom, l.geom)
                AND NOT ST_Contains(p.geom, l.geom)
), paths_expanded AS ( -- expand paths so we can order them
    SELECT
        array_to_string(ids, ',') AS path_variation_id,
        geom,
        degree,
        MAX(degree) OVER(PARTITION BY path_id) AS max_degree,
        UNNEST(ids) AS id
    FROM paths
), full_paths_ordered AS ( -- order full paths so we can remove duplicates
    SELECT path_variation_id, geom, ARRAY_AGG(id ORDER BY id) AS ids
    FROM paths_expanded
    WHERE degree = max_degree
    GROUP BY path_variation_id, geom
) -- remove duplicate paths
SELECT DISTINCT ON(ids) ids, ST_AsText(geom) AS wkt
FROM full_paths_ordered
ORDER BY ids, path_variation_id;