Question

是否可以重写此plpgsql过程以避免两次调用 json.get_user_notifications ？

CREATE OR REPLACE FUNCTION json.rowset_notifications(arg1 integer, arg2 integer, arg3 integer)
  RETURNS SETOF json.notification AS
$BODY$
DECLARE
  pmax_limit boolean;
BEGIN
  pmax_limit := (SELECT COUNT(*) > 200 FROM json.get_user_notifications($1, $2, $3));
  IF pmax_limit THEN
    RETURN QUERY SELECT n.* FROM json.get_compressed_user_notifications($1, $2, $3) n;
  ELSE
    RETURN QUERY SELECT n.* FROM json.get_user_notifications($1, $2, $3) n;
  END IF;
END
$BODY$
  LANGUAGE plpgsql STABLE
  COST 100
  ROWS 200;

类似的东西（当然它不起作用）：

WITH
    notifications AS (SELECT n.* FROM json.get_user_notifications($1, $2, $3) n LIMIT 201)
SELECT CASE
    WHEN COUNT(*) > 200 THEN
        RETURN QUERY SELECT n.* FROM json.get_compressed_user_notifications($1, $2, $3) n;
    ELSE
        RETURN QUERY SELECT n.* FROM notifications n;
    END
FROM notifications;

Answer 1

当然，像这样运行其他查询

SELECT n.*
FROM json.get_user_notifications($1, $2, $3) AS n
WHERE ( SELECT count(*)>200 FROM json.get_user_notifications )

你可能必须明确。如果返回，则可以返回json.notification的结果集。如果它没有返回，那么你知道你需要返回压缩的结果集。

Answer 2

你可能会寻找：

WITH notifications AS (
     SELECT n.*
       FROM json.get_user_notifications($1, $2, $3) n
      LIMIT 201
)
SELECT *
  FROM notifications
 WHERE (SELECT COUNT(*) <= 200 FROM notifications)
 UNION
SELECT *
  FROM json.get_compressed_user_notifications($1, $2, $3)
 WHERE (SELECT COUNT(*) > 200 FROM notifications)

如何重写postgresql程序以避免二次调用

2 个答案: