Question

我正在尝试使用POSTGRESQL中的WITH语句进行以下查询：

WITH catchment AS (
                SELECT *  FROM  ..   -- Some time consuming join statement
     ),
     catchment10 AS (
                SELECT * FROM pgr_pointsaspolygon('SELECT * FROM catchment where cost < 10000')
     ),
     catchment20 AS (
                SELECT * FROM pgr_pointsaspolygon('SELECT * FROM catchment where cost < 20000')
     ),
     catchment30 AS (
                SELECT * FROM pgr_pointsaspolygon('SELECT * FROM catchment where cost < 30000')
     )
SELECT * FROM  catchment10
UNION
SELECT * FROM  catchment20
UNION
SELECT * FROM  catchment30

问题是pgr_pointsaspolygon（）函数调用了pgr_alphashape（）函数，该函数使用了一些c库：

CREATE OR REPLACE FUNCTION pgr_alphashape(IN sql text, OUT x double precision, OUT y double precision)
  RETURNS SETOF record AS
'$libdir/librouting_dd', 'alphashape'
  LANGUAGE c IMMUTABLE STRICT
  COST 1
  ROWS 1000;
ALTER FUNCTION pgr_alphashape(text)
  OWNER TO postgres;

pgr_alphashape需要一个sql语句才能工作，但是当我从WITH子句传递catchment表时，它会出现以下错误：

      ERROR:  relation "catchment" does not exist

是否有任何其他方法或方法来纠正此错误，以便集水表不会被计算3次，但可以传递给pgr_pointsaspolygon函数？

Answer 1

由于您显然正在使用第三方提供的功能，因此您唯一的选择是临时表。将CREATE TABLE AS与ON COMMIT DROP一起使用可避免与同一会话中的多个呼叫冲突。

BEGIN;
CREATE TEMP TABLE catchment ON COMMIT DROP AS
SELECT *  FROM  ..   -- Some time consuming join statement
;

SELECT * FROM pgr_pointsaspolygon('SELECT * FROM catchment WHERE cost < 10000')
UNION ALL  -- Presuming we do not want to eliminate dupes?
SELECT * FROM pgr_pointsaspolygon('SELECT * FROM catchment WHERE cost < 20000')
UNION ALL
SELECT * FROM pgr_pointsaspolygon('SELECT * FROM catchment WHERE cost < 30000')
COMMIT;

Postgresql WITH语句与c函数一起使用，需要sql文本作为参数

1 个答案: