sql – 在Postgres中查询的高效时间序列

我的PG数据库中有一个表,看起来有点像这样：

id | widget_id | for_date | score |

每个引用的小部件都有很多这些项目.每个小部件每天总是1个,但是存在差距.

我想得到的结果是包含自X以来每个日期的所有小部件.日期通过生成系列引入：

SELECT date.date::date
   FROM generate_series('2012-01-01'::timestamp with time zone,'Now'::text::date::timestamp with time zone,'1 day') date(date)
 ORDER BY date.date DESC;

如果没有给定widget_id的日期条目,我想使用前一个.所以说小工具1337在2012-05-10没有条目,但在2012-05-08,那么我希望结果集在2012-05-10也显示2012-05-08条目：

Actual data:
widget_id | for_date   | score
1312      | 2012-05-07 | 20
1337      | 2012-05-07 | 12
1337      | 2012-05-08 | 41
1337      | 2012-05-11 | 500

Desired output based on generate series:
widget_id | for_date   | score
1336      | 2012-05-07 | 20
1337      | 2012-05-07 | 12
1336      | 2012-05-08 | 20
1337      | 2012-05-08 | 41
1336      | 2012-05-09 | 20
1337      | 2012-05-09 | 41
1336      | 2012-05-10 | 20
1337      | 2012-05-10 | 41
1336      | 2012-05-11 | 20
1337      | 2012-05-11 | 500

最终我想把它归结为一个视图,所以我每天都有一致的数据集,我可以轻松查询.

编辑：使样本数据和预期结果集更清晰

解决方法

SQL Fiddle

select
    widget_id,for_date,case
        when score is not null then score
        else first_value(score) over (partition by widget_id,c order by for_date)
        end score
from (
    select
        a.widget_id,a.for_date,s.score,count(score) over(partition by a.widget_id order by a.for_date) c
    from (
        select widget_id,g.d::date for_date
        from (
            select distinct widget_id
            from score
            ) s
            cross join
            generate_series(
                (select min(for_date) from score),(select max(for_date) from score),'1 day'
            ) g(d)
        ) a
        left join
        score s on a.widget_id = s.widget_id and a.for_date = s.for_date
) s
order by widget_id,for_date