如何动态连接多个聚合查询的输出？

Question

我正在构建一个 Postgres 查询，它需要对数组中的每个条目调用一个聚合函数，然后将所有这些聚合值连接在一起。

这是对其中一个聚合的查询：

WITH mvtdata AS
(
  SELECT ST_AsMVTGeom(geom, ST_TileEnvelope(12,513,412)) AS geom, name, description
  FROM feature
  WHERE feature_set = 'river'
    AND ST_Intersects(geom, ST_TileEnvelope(12,513,412))
)
SELECT ST_AsMVT(mvtdata.*, 'river')
FROM mvtdata;

我有一个单独的表来定义不同的数据层。每个数据层都需要调用上述查询并连接其结果。

假设我有一个具有以下值的 layer 表（如果更简单，我也可以使用数组）：

|  name        |
|  'river'     |
|  'building'  |

我想为表中的每个条目调用一次上述查询并将值连接起来。比如：

WITH riverdata AS
(
  SELECT ST_AsMVTGeom(geom, ST_TileEnvelope(12,513,412)) AS geom, name, description
  FROM feature
  WHERE feature_set = 'river'
    AND ST_Intersects(geom, ST_TileEnvelope(12,513,412))
),
buildingdata AS
(
  SELECT ST_AsMVTGeom(geom, ST_TileEnvelope(12,513,412)) AS geom, name, description
  FROM feature
  WHERE feature_set = 'building'
    AND ST_Intersects(geom, ST_TileEnvelope(12,513,412))
)
SELECT (ST_AsMVT(riverdata.*, 'river') || ST_AsMVT(buildingdata.*, 'building')) mvt
FROM riverdata, buildingdata;

如何编写查询以使用这样的表（或数组）动态连接任意数量的数据层？每层有一个单独的ST_AsMVT() 调用很重要。

Answer 1

您可以简单地将键值放入IN 子句中，这样您就可以在一个查询中获得所有需要的记录。之后，获取CTE检索到的记录，并应用ST_AsMVT函数。

WITH mvtdata AS
(
  SELECT 
    ST_AsMVTGeom(geom, ST_TileEnvelope(12,513,412)) AS geom, 
    name, description,feature_set
  FROM feature
  WHERE feature_set IN ('river','building')
    AND ST_Intersects(geom, ST_TileEnvelope(12,513,412))
)
SELECT 
  ST_AsMVT(mvtdata.*,feature_set)
FROM mvtdata

如果您更喜欢使用数组，请将IN 替换为ANY/SOME，例如：

WHERE feature_set = ANY ('{river,building}')

如果仍然没有帮助，看看plpgsql可能会很有趣：

CREATE OR REPLACE FUNCTION public.concat_mvt(arr_feature TEXT[]) 
RETURNS BYTEA LANGUAGE plpgsql 
AS $BODY$
DECLARE 
  i INTEGER;
  res BYTEA DEFAULT '';
  rec BYTEA;
BEGIN 
FOR i IN 1..array_length(arr_feature,1) LOOP
  WITH mvtdata AS (
  SELECT 
    ST_AsMVTGeom(geom, ST_TileEnvelope(12,513,412)) AS geom, 
    name, description,feature_set
  FROM feature
  WHERE feature_set = arr_feature[i]
    AND ST_Intersects(geom, ST_TileEnvelope(12,513,412))
  ) SELECT ST_AsMVT(mvtdata.*,arr_feature[i])
    FROM mvtdata INTO rec;
  res := res || rec;
END LOOP;
RETURN res;
END $BODY$;

.. 像这样调用函数

SELECT concat_mvt('{river,building}')