Question

我有一个想在postgresql函数中使用的回溯查询，它应该返回一个布尔值。

CREATE OR REPLACE FUNCTION store.is_item(object1 VARCHAR(40), object2 VARCHAR(40))
RETURNS BOOLEAN AS $$
BEGIN
   WITH RECURSIVE externals AS (
   SELECT object_id, used_id
   FROM store.obj_depend
   WHERE external = true
   ), history AS (
   SELECT content_id AS id
   FROM store.minfos
   WHERE id= $2
   UNION
   SELECT externals.used_id
   FROM externals
   INNER JOIN history ON history.id = externals.object_id
   ),
   PERFORM (SELECT c.id FROM store.cinfo AS c WHERE c.id = $1 INNER JOIN history 
   ON c.id = history.id);
   RETURN FOUND;
END;
$$ LANGUAGE plpgsql;

当我尝试这样做时，出现错误syntax error at or near SELECT

Answer 1

PERFORM是plpgsql语句，不能在任何SQL命令中使用。

您可以像建议的@klin一样使用PERFORM，但是随后在子查询中使用CTE，并且子查询每次都返回一行。那么FOUND变量每次都应该为true。

在这种情况下，最好使用辅助变量作为目标。

CREATE OR REPLACE FUNCTION store.is_item(object1 VARCHAR(40), object2 VARCHAR(40))
RETURNS BOOLEAN AS $$
DECLARE r record;
BEGIN
  WITH RECURSIVE 
    externals AS (SELECT object_id, used_id
                    FROM store.obj_depend
                   WHERE external = true)
    history AS (SELECT content_id AS id
                  FROM store.minfos
                 WHERE id = object2
                UNION
                SELECT externals.used_id
                  FROM externals
                       INNER JOIN history ON history.id = externals.object_id)
  SELECT c.id
    FROM store.cinfo AS c 
         INNER JOIN history ON c.id = history.id
   WHERE c.id = $1 
    INTO r;
  RETURN FOUND;
END;
$$ LANGUAGE plpgsql;

在PostgreSQL中的递归查询函数中使用PERFORM

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