Question

我有SELECT：

SELECT month, year, ROUND(AVG(q_overall) OVER (rows BETWEEN 10000 preceding and current row),2) as avg 
FROM (
  SELECT EXTRACT(Month FROM date) as month, EXTRACT(Year FROM date) as year, ROUND(AVG(q_overall),1) as q_overall 
  FROM fb_parsed 
  WHERE business_id = 1
  GROUP BY year, month
  ORDER BY year, month) a

输出：

 month  year  avg       
 ----------------- 
 12     2012  5 
 1      2013  4.5
 2      2013  4.1
 4      2013  4.8
 5      2013  4.7

我必须在附表中附上缺失值（在本例中为2013年的第3个月）。平均值必须与前一行相同，这意味着我需要将此表附加到：

 3      2013  4.1

我可以使用SELF JOINS和generate_series，还是使用某些UNION选择？

Answer 1

您可以简化选择。它不需要子查询：

SELECT EXTRACT(Month FROM date) as month,
       EXTRACT(Year FROM date) as year,
       ROUND(AVG(q_overall), 1) as q_overall,
       ROUND(AVG(AVG(q_overall)) OVER (rows BETWEEN 10000 preceding and current row), 2)
FROM fb_parsed 
WHERE business_id = 1
GROUP BY year, month;

Windows功能需要order by。我假设你真的打算：

SELECT EXTRACT(Month FROM date) as month,
       EXTRACT(Year FROM date) as year,
       ROUND(AVG(q_overall), 1) as q_overall,
       ROUND(AVG(AVG(q_overall)) OVER (ORDER BY year, month)), 2)
FROM fb_parsed 
WHERE business_id = 1
GROUP BY year, month;

然后，要填写值，您可以使用generate_series()：

SELECT EXTRACT(Month FROM ym.date) as month,
       EXTRACT(Year FROM ym.date) as year,
       ROUND(AVG(AVG(q_overall)) OVER (ORDER BY year, month)), 2)
FROM (SELECT generate_series(date_trunc('month', min(date)),
                             date_trunc('month', max(date)),
                             interval '1 month') as date
      FROM fb_parsed 
     ) ym LEFT JOIN
     fb_parsed p
     ON EXTRACT(year FROM ym.date) = EXTRACT(year FROM p.date) AND
        EXTRACT(month FROM ym.date) = EXTRACT(month FROM p.date) AND
        p.business_id = 1
GROUP BY year, month;

我认为这会做你想要的。

Answer 2

我可以使用SELF JOINS和generate_series吗？

是的，您已关闭，但您当前的查询会产生累积平均值。棘手的部分是用前一个值填补空白（如果PostgreSQL支持IGNORE NULLS的{{1}}选项，这会更容易......）

LAST_VALUE

编辑：

哎呀，这太复杂了，问题是累积平均值然后NULL不会改变结果而且填补空白

Answer 3

最终查询：

update products
    set sales_tax = buyPrice * 0.08
    where sales_tax is null;

使用缺少的月份和年份值附加选择

3 个答案: