标记不连续的日期范围

Question

背景(输入)

在全球历史气候网络已其收藏的天气测量的标记无效或错误的数据.删除这些元素后,有大量数据不再具有连续的日期部分.数据类似于:

"2007-12-01";14 -- Start of December
"2007-12-29";8
"2007-12-30";11
"2007-12-31";7
"2008-01-01";8 -- Start of January
"2008-01-02";12
"2008-01-29";0
"2008-01-31";7
"2008-02-01";4 -- Start of February
... entire month is complete ...
"2008-02-29";12
"2008-03-01";14  -- Start of March
"2008-03-02";17
"2008-03-05";17

问题(输出)

虽然可以推断缺失的数据(例如,通过平均其他年份)来提供连续的范围,但为了简化系统,我想根据是否有一个连续的日期范围填写月份来标记非连续的段:

D;"2007-12-01";14 -- Start of December
D;"2007-12-29";8
D;"2007-12-30";11
D;"2007-12-31";7
D;"2008-01-01";8 -- Start of January
D;"2008-01-02";12
D;"2008-01-29";0
D;"2008-01-31";7
"2008-02-01";4 -- Start of February
... entire month is complete ...
"2008-02-29";12
D;"2008-03-01";14  -- Start of March
D;"2008-03-02";17
D;"2008-03-05";17

一些测量是在1843年进行的.

题

对于所有气象站,您如何标记缺少一天或多天的所有日期？

源代码

选择数据的代码类似于:

select
  m.id,
  m.taken,
  m.station_id,
  m.amount
from
  climate.measurement

相关的想法

生成一个填充了连续日期的表,并将它们与测量数据日期进行比较.

• 在sql结果中填充空日期的最简单方法是什么(在mysql或perl端)？
• 如何对连续范围进行分组
• http://msdn.microsoft.com/en-us/library/aa175780%28v=sql.80%29.aspx

更新

可以使用本节中的SQL重新创建该问题.

表

该表创建如下:

CREATE TABLE climate.calendar
(
  id serial NOT NULL,
  n character varying(2) NOT NULL,
  d date NOT NULL,
  "valid" boolean NOT NULL DEFAULT true,
  CONSTRAINT calendar_pk PRIMARY KEY (id)
)
WITH (
  OIDS=FALSE
);

生成数据

以下SQL将数据插入表(id[int],name [varchar],date [date],valid[boolean]):

insert into climate.calendar (n, d) 
    select 'A', (date('1982-01-1') + (n || ' days')::interval)::date cal_date
    from generate_series(0, date('2011-04-9') - date('1982-01-1') ) n
insert into climate.calendar (n, d) 
    select 'B', (date('1982-01-1') + (n || ' days')::interval)::date cal_date
    from generate_series(0, date('2011-04-9') - date('1982-01-1') ) n
insert into climate.calendar (n, d) 
    select 'C', (date('1982-01-1') + (n || ' days')::interval)::date cal_date
    from generate_series(0, date('2011-04-9') - date('1982-01-1') ) n
insert into climate.calendar (n, d) 
    select 'D', (date('1982-01-1') + (n || ' days')::interval)::date cal_date
    from generate_series(0, date('2011-04-9') - date('1982-01-1') ) n
insert into climate.calendar (n, d) 
    select 'E', (date('1982-01-1') + (n || ' days')::interval)::date cal_date
    from generate_series(0, date('2011-04-9') - date('1982-01-1') ) n
insert into climate.calendar (n, d) 
    select 'F', (date('1982-01-1') + (n || ' days')::interval)::date cal_date
    from generate_series(0, date('2011-04-9') - date('1982-01-1') ) n

值'A'通过'F'表示在特定日期进行测量的气象站的名称.

删除随机行

删除一些行如下:

delete from climate.calendar where id in (select id from climate.calendar order by random() limit 5000);

尝试#1

下列不切换的valid标志,false在一个月的所有天,其中一个月是缺少一个或多个天:

UPDATE climate.calendar
SET valid = false
WHERE date_trunc('month', d) IN (
    SELECT DISTINCT date_trunc('month', d)
    FROM climate.calendar A
    WHERE NOT EXISTS (
        SELECT 1
        FROM climate.calendar B
        WHERE A.d - 1 = B.d
   )
);

尝试#2

以下SQL生成一个空结果集:

with gen_calendar as (
    select (date('1982-01-1') + (n || ' days')::interval)::date cal_date
    from generate_series(0, date('2011-04-9') - date('1982-01-1') ) n
)
select gc.cal_date
from gen_calendar gc
left join climate.calendar c on c.d = gc.cal_date
where c.d is null;

尝试#3

以下SQL生成了站名和日期的所有可能组合:

select
  distinct( cc.n ), t.d
from
  climate.calendar cc,
  (
    select (date('1982-01-1') + (n || ' days')::interval)::date d
    from generate_series(0, date('2011-04-9') - date('1982-01-1') ) n
  ) t
order by
  cc.n

然而,在真实数据中有几百个站,日期可以追溯到19世纪中期,因此所有站的所有日期的笛卡尔都太大了.如果有足够的时间,这样的方法可能会有效......必须有更快的方法.

尝试#4

PostgreSQL具有窗口函数.

如何使用postgres中的窗口函数选择特定的更改

谢谢!

Answer 1

generate_series()

PostgreSQL 的generate_series()函数可以创建一个包含连续日期列表的视图：

with calendar as (
    select ((select min(date) from test)::date + (n || ' days')::interval)::date cal_date
    from generate_series(0, (select max(date) - min(date) from test)) n
)
select cal_date
from calendar c
left join test t on t.date = c.cal_date
where t.date is null;

表达式select max(date) - min(date) from test可能相差一个。

计算每月的天数

识别无效月份的一种方法是创建两个视图。第一个计算每个站点每个月应该产生的每日读数数量。（注意climate.calendar转换为climate_calendar。）第二个返回每个站点每月产生的实际每日读数。

每个站点每月最多天数

此视图将返回每个站点一个月中的实际天数。（例如，二月总是有 28 或 29 天。）

create view count_max_station_calendar_days as 
with calendar as (
    select ((select min(d) from climate_calendar)::date + (n || ' days')::interval)::date cal_date
    from generate_series(0, (select max(d) - min(d) from climate_calendar)) n
)
select n, extract(year from cal_date) yr, extract(month from cal_date) mo, count(*) num_days
from stations cross join calendar
group by n, yr, mo
order by n, yr, mo

每个站点每月实际天数

返回的总天数将少于计数。（例如，一月将始终有 31 天或更少。）

create view count_actual_station_calendar_days as
select n, extract(year from d) yr, extract(month from d) mo, count(*) num_days
from climate_calendar
group by n, yr, mo
order by n, yr, mo;

删除ORDER BY生产中的条款（它们有助于开发）。

比较视图

将两个视图连接起来，将需要标记的站点和月份标识到一个新视图中：

create view invalid_station_months as 
select m.n, m.yr, m.mo, m.num_days - a.num_days num_days_missing
from count_max_station_calendar_days m
inner join count_actual_station_calendar_days a
       on (m.n = a.n and m.yr = a.yr and m.mo = a.mo and m.num_days <> a.num_days)

n   yr    mo  num_days_missing
--
A   1982  1   1
E   2007  3   1

该列num_days_missing不是必需的，但很有用。

这些是需要更新的行：

select cc.* 
from climate_calendar cc
inner join invalid_station_months im 
        on (cc.n = im.n and 
            extract(year from cc.d) = im.yr and
            extract(month from cc.d) = im.mo)
where valid = true

更新数据库

要更新它们，id关键是方便。

update climate_calendar
set valid = false
where id in (
    select id
    from climate_calendar cc
    inner join invalid_station_months im 
        on (cc.n = im.n and 
            extract(year from cc.d) = im.yr and
            extract(month from cc.d) = im.mo)
    where valid = true
);