Question

我有一个有关类别（价格，视图，设施，位置）的露营地的评论表。以下查询用于按平均四个类别显示前20个评论。

SELECT
  ROUND(((R.price + R.location + R.facilities + R.view) / 4), 2) AS avg,
  R.poi_id,
  poi.Name
FROM
  `Reviews` AS `R`
  LEFT JOIN `poi` ON `R`.`poi_id` = `poi`.`ID`
ORDER BY avg DESC
LIMIT 20

但是我已经意识到查询不适合同一个露营地有多个评论的情况。

那么有一个查询会返回最高的20个评级露营地（poi），其中包含该poiID的平均价格，视图，设施，位置/评论数量？

Answer 1

平均功能当然是累积的，但你可以通过SUM评论分数和COUNT他们的数字来实现它：

SELECT
  ROUND(((R.price + R.location + R.facilities + R.view) / 4 * cnt), 2) AS avg,
  R.poi_id,
  poi.Name
FROM
  (SELECT SUM(price) AS price, 
          SUM(location) AS location,
          SUM(facilities) AS facilities,
          SUM(view) AS view,
          COUNT(*) AS cnt,
          poi_id
   FROM   Review
   GROUP BY poi_id) AS `R`
  LEFT JOIN `poi` ON `R`.`poi_id` = `poi`.`ID`
ORDER BY avg DESC
LIMIT 20

获取一组记录的平均值

1 个答案: