我的PG数据库中有一张表看起来像这样：
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，但也有差距。
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。所以说小部件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。
修改：使示例数据和预期结果集更加清晰
答案 0 :(得分：8)
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
答案 1 :(得分：7)
首先，你可以有一个更简单的generate_series()表表达式。相当于你的（除了降序，这与你的其余问题相矛盾）：
SELECT generate_series('2012-01-01'::date, now()::date, '1d')::date
类型date会在输入时自动强制为timestamptz。无论哪种方式，返回类型都是timestamptz。我在下面使用子查询，因此我可以立即将输出转换为date。
下一步，max()作为窗口函数准确返回您需要的内容：自 frame 开始忽略NULL值以来的最高值。在此基础上，您可以获得极其简单的查询。
最有可能比涉及CROSS JOIN或WITH RECURSIVE：
SELECT a.day, s.*
FROM (
SELECT d.day
,max(s.for_date) OVER (ORDER BY d.day) AS effective_date
FROM (
SELECT generate_series('2012-01-01'::date, now()::date, '1d')::date
) d(day)
LEFT JOIN score s ON s.for_date = d.day
AND s.widget_id = 1337 -- "for a given widget_id"
) a
LEFT JOIN score s ON s.for_date = a.effective_date
AND s.widget_id = 1337
ORDER BY a.day;
使用此查询，您可以将您喜欢的score列添加到最终的SELECT列表中。我把s。*简单化了。选择你的专栏。
如果您想在实际 得分的第一天开始输出，只需将上一个LEFT JOIN替换为JOIN。
在这里，我使用CROSS JOIN为每个日期的每个小部件生成一行..
SELECT a.day, a.widget_id, s.score
FROM (
SELECT d.day, w.widget_id
,max(s.for_date) OVER (PARTITION BY w.widget_id
ORDER BY d.day) AS effective_date
FROM (SELECT generate_series('2012-05-05'::date
,'2012-05-15'::date, '1d')::date AS day) d
CROSS JOIN (SELECT DISTINCT widget_id FROM score) AS w
LEFT JOIN score s ON s.for_date = d.day AND s.widget_id = w.widget_id
) a
JOIN score s ON s.for_date = a.effective_date
AND s.widget_id = a.widget_id -- instead of LEFT JOIN
ORDER BY a.day, a.widget_id;
答案 2 :(得分：2)
使用您的表结构，我创建了以下递归CTE，它以MIN（For_Date）开始并递增，直到达到MAX（For_Date）。不确定是否有更有效的方法，但这似乎运作良好：
WITH RECURSIVE nodes_cte(widgetid, for_date, score) AS (
-- First Widget Using Min Date
SELECT
w.widgetId,
w.for_date,
w.score
FROM widgets w
INNER JOIN (
SELECT widgetId, Min(for_date) min_for_date
FROM widgets
GROUP BY widgetId
) minW ON w.widgetId = minW.widgetid
AND w.for_date = minW.min_for_date
UNION ALL
SELECT
n.widgetId,
n.for_date + 1 for_date,
coalesce(w.score,n.score) score
FROM nodes_cte n
INNER JOIN (
SELECT widgetId, Max(for_date) max_for_date
FROM widgets
GROUP BY widgetId
) maxW ON n.widgetId = maxW.widgetId
LEFT JOIN widgets w ON n.widgetid = w.widgetid
AND n.for_date + 1 = w.for_date
WHERE n.for_date + 1 <= maxW.max_for_date
)
SELECT *
FROM nodes_cte
ORDER BY for_date
这是SQL Fiddle。
返回的结果（按照您的喜好格式化日期）：
WIDGETID FOR_DATE SCORE
1337 May, 07 2012 00:00:00+0000 12
1337 May, 08 2012 00:00:00+0000 41
1337 May, 09 2012 00:00:00+0000 41
1337 May, 10 2012 00:00:00+0000 41
1337 May, 11 2012 00:00:00+0000 500
请注意，这假设您的For_Date字段是日期 - 如果它包含时间 - 那么您可能需要在上面的查询中使用Interval“1天”。
希望这有帮助。
答案 3 :(得分：0)
数据：
DROP SCHEMA tmp CASCADE;
CREATE SCHEMA tmp ;
SET search_path=tmp;
CREATE TABLE widget
( widget_id INTEGER NOT NULL
, for_date DATE NOT NULL
, score INTEGER
, PRIMARY KEY (widget_id,for_date)
);
INSERT INTO widget(widget_id , for_date , score) VALUES
(1312, '2012-05-07', 20)
, (1337, '2012-05-07', 12)
, (1337, '2012-05-08', 41)
, (1337, '2012-05-11', 500)
;
查询：
SELECT w.widget_id AS widget_id
, cal::date AS for_date
-- , w.for_date AS org_date
, w.score AS score
FROM generate_series( '2012-05-07'::timestamp , '2012-05-11'::timestamp
, '1day'::interval) AS cal
-- "half cartesian" Join;
-- will be restricted by the NOT EXISTS() below
LEFT JOIN widget w ON w.for_date <= cal
WHERE NOT EXISTS (
SELECT * FROM widget nx
WHERE nx.widget_id = w.widget_id
AND nx.for_date <= cal
AND nx.for_date > w.for_date
)
ORDER BY cal, w.widget_id
;
结果：
widget_id | for_date | score
-----------+------------+-------
1312 | 2012-05-07 | 20
1337 | 2012-05-07 | 12
1312 | 2012-05-08 | 20
1337 | 2012-05-08 | 41
1312 | 2012-05-09 | 20
1337 | 2012-05-09 | 41
1312 | 2012-05-10 | 20
1337 | 2012-05-10 | 41
1312 | 2012-05-11 | 20
1337 | 2012-05-11 | 500
(10 rows)