Question

我是PostgreSQL和本网站的新手。我需要你的帮助。

我需要获得超过平均降雨量的所有月份。

我尝试了这个，但它不起作用，有人可以解释一下吗？

Select month, rain from weather 
where rain > avg(rain)
group by month , rain;

非常感谢。

Answer 1

试试这个

SELECT month FROM (SELECT month, avg(rain) avg_rain FROM weather GROUP BY month) a
CROSS JOIN
(SELECT avg(rain) rain FROM weather) b
WHERE avg_rain > rain

Answer 2

WITH rain_avg_by_month AS (
  SELECT month, AVG(rain) AS rain_avg
  FROM weather
  GROUP BY month
), total_rain_avg AS (
  SELECT AVG(rain_avg)
  FROM rain_avg_by_month
)
SELECT month
FROM rain_avg_by_month, total_rain_avg
WHERE rain_avg_by_month.rain_avg > total_rain_avg.avg
;

Answer 3

select * from (
    select
            month,
            rain,
            avg(rain) over() avg_rain
        from weather
    ) t
    where rain > avg_rain;

这里我们假设每月有一条记录。第一个查询（嵌套的）给出了所有月份和相应的降雨值以及平均降雨量值（我们对集合中的所有记录使用窗口函数avg）。然后外部查询给出了我们所需要的：雨量值大于平均降雨量的月份。

我如何获得比平均值更大的结果（我不具备的平均值）？

3 个答案: