我想得到的是每月从generate_series开始的统计数据以及每个月计算的id的总和。这个SQL适用于PostgreSQL 9.1:
SELECT (to_char(serie,'yyyy-mm')) AS year, sum(amount)::int AS eintraege FROM (
SELECT
COUNT(mytable.id) as amount,
generate_series::date as serie
FROM mytable
RIGHT JOIN generate_series(
(SELECT min(date_from) FROM mytable)::date,
(SELECT max(date_from) FROM mytable)::date,
interval '1 day') ON generate_series = date(date_from)
WHERE version = 1
GROUP BY generate_series
) AS foo
GROUP BY Year
ORDER BY Year ASC;
这是我的输出
"2006-12" | 4
"2007-02" | 1
"2007-03" | 1
但我想得到的是这个输出(1月份的“0”值):
"2006-12" | 4
"2007-01" | 0
"2007-02" | 1
"2007-03" | 1
因此,如果有一个月没有id,那么它应该被列出。任何想法如何解决这个问题?
以下是一些示例数据:
drop table if exists mytable;
create table mytable(id bigint, version smallint, date_from timestamp without time zone);
insert into mytable(id, version, date_from) values
('4084036', '1', '2006-12-22 22:46:35'),
('4084938', '1', '2006-12-23 16:19:13'),
('4084938', '2', '2006-12-23 16:20:23'),
('4084939', '1', '2006-12-23 16:29:14'),
('4084954', '1', '2006-12-23 16:28:28'),
('4250653', '1', '2007-02-12 21:58:53'),
('4250657', '1', '2007-03-12 21:58:53')
;
解开,简化和修复,它可能看起来像这样:
SELECT to_char(s.tag,'yyyy-mm') AS monat
, count(t.id) AS eintraege
FROM (
SELECT generate_series(min(date_from)::date
, max(date_from)::date
, interval '1 day'
)::date AS tag
FROM mytable t
) s
LEFT JOIN mytable t ON t.date_from::date = s.tag AND t.version = 1
GROUP BY 1
ORDER BY 1;
db <>小提琴here
在所有噪音,误导性标识符和非常规格式中,实际问题隐藏在此处:
WHERE version = 1
当你正确使用RIGHT [OUTER] JOIN
时,你通过添加一个WHERE
条款取消了这一努力,该条款要求mytable
有效地将RIGHT JOIN
转换为JOIN
。
将该条款拉入JOIN
条件以使其工作。
我简化了其他一些事情。
有关: