在PostgreSQL中获取具有不一致数据的移动平均值

Question

我有一个名为answers的表，列created_at和response，响应是整数0（表示'no'），1（表示'是'），或2（表示'不知道'）。我希望获得响应值的移动平均值，每天过滤掉2个，只考虑前30天。我知道你可以做ROWS BETWEEN 29 AND PRECEDING AND CURRENT ROW，但只有你每天都有数据才有效，而在我的情况下，可能没有一周或更长时间的数据。

我目前的查询是这样的：

SELECT answers.created_at, answers.response,
    AVG(answers.response)
      OVER(ORDER BY answers.created_at::date ROWS 
        BETWEEN 29 PRECEDING AND CURRENT ROW) AS rolling_average
  FROM answers
  WHERE answers.user_id = 'insert_user_id'' 
    AND (answers.response = 0 OR answers.response = 1)
  GROUP BY answers.created_at, answers.response
  ORDER BY answers.created_at::date

但是这将返回基于之前行的平均值，如果用户在1上使用2018-3-30并在0上使用2018-5-15，则2018-5-15的滚动平均值将是0.5而不是0。如何创建一个查询，该查询仅考虑在过去30天内为滚动平均值创建的响应？

Answer 1

尝试这样的事情：

SELECT * FROM ( 
    SELECT 
        d.created_at, d.response, 
        Avg(d.response) OVER(ORDER BY d.created_at::date rows BETWEEN 29 PRECEDING AND CURRENT row) AS rolling_average 
    FROM ( 
        SELECT 
            COALESCE(a.created_at, d.dates) AS created_at, response, a.user_id 
        FROM 
            (SELECT generate_series('2018-01-01'::date, '2018-05-31'::date, '1day'::interval)::date AS dates) d 
        LEFT JOIN 
            (SELECT * FROM answers WHERE answers.user_id = 'insert_user_id' AND ( answers.response = 0 OR answers.response = 1)) a 
        ON d.dates = a.created_at::date 
    ) d 
    GROUP BY d.created_at, d.response 
) agg WHERE agg.response IS NOT NULL 
ORDER BY agg.created_at::date

• generate_series创建日期列表 - 您必须设置合理的边界
• 这个日期列表是LEFT JOINED和预先选择的答案
• 该结果用于滚动平均计算
• 在它之后我只选择带有响应的记录，我得到：

created_at | response | rolling_averagte 
2018-03-30 | 1        | 1.00000000000000000000 
2018-05-15 | 0        | 0.00000000000000000000

Answer 2

从Postgres 11开始，您可以这样做：

SELECT created_at, 
       response,
       AVG(response) OVER (ORDER BY created_at 
                           RANGE BETWEEN '29 day' PRECEDING AND current row) AS rolling_average 
FROM answers
WHERE user_id = 1
  AND response in (0,1)
ORDER BY created_at;