Question

这篇文章与another question of mine有关。我提出了一个基本上我想要的递归查询。只要dist_calc_points属性的计数未超过，就会执行递归查询。但这仅适用于一个条目（请参阅WHERE v2_channel.id=2子句）。我如何将此查询应用于整个表？

WITH RECURSIVE dist(x, the_geom, d) AS (
    SELECT 
       0::double precision, 
       the_geom, 
       0::double precision 
    FROM v2_channel where v2_channel.id=2
       UNION ALL
    SELECT 
      x+1, 
      v2_channel.the_geom AS gm, 
      d+(1/v2_channel.dist_calc_points) AS dist_calc_pnts 
    FROM v2_channel, dist 
      WHERE dist.x<v2_channel.dist_calc_points AND v2_channel.id=2
)
SELECT *, ST_AsText(ST_LineInterpolatePoint(the_geom, d)) FROM dist;

Answer 1

要允许CTE应用于多行，您必须能够识别这些行。所以只需添加ID：

WITH RECURSIVE dist(id, x, the_geom, d) AS (
    SELECT
       id,
       0::double precision,
       the_geom,
       0::double precision
    FROM v2_channel
       UNION ALL
    SELECT
      dist.id,
      x+1,
      v2_channel.the_geom AS gm,
      d+(1/v2_channel.dist_calc_points) AS dist_calc_pnts
    FROM v2_channel JOIN dist
        ON  dist.x  < v2_channel.dist_calc_points
        AND dist.id = v2_channel.id
)
SELECT *, ST_AsText(ST_LineInterpolatePoint(the_geom, d)) FROM dist;

如何将递归查询应用于整个表？

1 个答案: