sql - 从具有 postgres 一年记录的数据库中获取按月数据

Question

我有一个包含以下列的年份数据的表：

Table "myData" ((
    "Status" character varying,  
    "Project" character varying,  
    "Product" character varying, 
    "Identifier" character varying, 
    "Submittedon" date
    )

ETC。，

现在获取在特定月份提交的记录计数。比如说 2013 年 4 月的记录计数，我正在使用：

select count("Status") as April2013 
from "myData"  
where (
    "SubmittedOn" > (current_date - 90) 
    and "SubmittedOn" < (current_date - 60)
)

结果：

April2013
--------
62

现在我的要求是获取过去 6 个月的记录数。我的意思是我希望我的输出采用以下任何一种格式：

FORMAT 1:

FORMAT 2:

6MonthsCount
-------------
34

23

44

41

18

9

Answer 1

select
    date_trunc('month', submittedOn) "month",
    count("Status") total
from "myData"  
group by 1
order by 1

Answer 2

这看起来像一个“数据透视”表，因此请使用 tablefunc 扩展的 crosstab() 函数（http://www.postgresql.org/docs/current/static/tablefunc.html）：

CREATE TABLE mydata (status text, submitteton date);
INSERT INTO mydata VALUES ('a', '2013-01-02'), ('b', '2013-01-05'), ('c', '2013-02-09'), ('d', '2013-04-11');


SELECT extract(month from submitteton) as month, count(*) FROM mydata GROUP BY month;
 month | count 
-------+-------
     1 |     2
     2 |     1
     4 |     1

CREATE EXTENSION tablefunc;
SELECT 
  *
FROM 
  crosstab(
    'SELECT 
       extract(year from submitteton)::int as year,
       extract(month from submitteton) as month, 
       count(*)::int 
     FROM
       mydata 
     GROUP BY 1,2 
     ORDER BY 1,2', 

     'SELECT * FROM generate_series(1, 12)'
  ) as ct(
    year int,
    jan int, feb int, mar int, apr int, may int, jun int, 
    jul int, aug int, sep int, oct int, nov int, dec int
  )
ORDER BY 
  year
;

 year | jan | feb | mar | apr | may | jun | jul | aug | sep | oct | nov | dec 
------+-----+-----+-----+-----+-----+-----+-----+-----+-----+-----+-----+-----
 2013 |   2 |   1 |     |   1 |     |     |     |     |     |     |     |    

Answer 3

您应该使用间隔和 date_trunc，而不是明确的天数：

denis=# select date_trunc('month', now()) as d;
           d            
------------------------
 2013-06-01 00:00:00+02
(1 row)

denis=# select date_trunc('month', now()) - interval '2 months' as d;
           d            
------------------------
 2013-04-01 00:00:00+02
(1 row)

要生成过去 6 个月，请使用generate_series()：

denis=# select d as start, d + interval '1 month' as stop
        from generate_series(date_trunc('month', now()) - interval '6 month',
                             date_trunc('month', now()),
                             '1 month') d;
         start          |          stop          
------------------------+------------------------
 2012-12-01 00:00:00+01 | 2013-01-01 00:00:00+01
 2013-01-01 00:00:00+01 | 2013-02-01 00:00:00+01
 2013-02-01 00:00:00+01 | 2013-03-01 00:00:00+01
 2013-03-01 00:00:00+01 | 2013-04-01 00:00:00+02
 2013-04-01 00:00:00+02 | 2013-05-01 00:00:00+02
 2013-05-01 00:00:00+02 | 2013-06-01 00:00:00+02
 2013-06-01 00:00:00+02 | 2013-07-01 00:00:00+02
(7 rows)

http://www.postgresql.org/docs/current/static/functions-srf.html

从那里，一个简单的加入计数/分组将产生预期的结果。

（注意：如果您需要没有时区的时间戳，请替换now()为例如(now() at time zone 'utc')::timestamp(0)