Question

我有一个Shipments表，其中基本上包含日期

的货件数据

id为integer datehipped是date

id    dateshipped
1     1-JAN-16
2     1-JAN-16
3     3-FEB-16
4     9-FEB-16

我想写一个查询，根据Months计算所有货件。我应该得到的是：

Jan  Feb  March....
2     2     0

我知道我可以通过查询每一列来实现它，只获得这个特定月份的相关行并计算它们。

如下：

Select     (Select count(*)
           from Shipments
           Where EXTRACT(YEAR FROM dateshipped)::int=2016 and EXTRACT(MONTH FROM dateshipped)::int=1 )as JAN,
           (Select count(*)
           from Shipments
           Where EXTRACT(YEAR FROM dateshipped)::int=2016 and EXTRACT(MONTH FROM dateshipped)::int=2 )as FEB

但是它的代码太多了......

如果可以使用单个FROM语句进行操作，并且每列都会获得它自己的相关行数，那么我很想知道。

类似的东西：

Select COL1,COL2,COL3...
from Shipments
Where EXTRACT(YEAR FROM dateshipped)::int=2016;

并且有类似的内容：

COL1 = count only JAN records
COL2 = count only FEB records
....

或许在几个月或其他任何解决方案上都有Parations的东西？

Answer 1

您需要一个透视查询来完成此任务：

SELECT SUM(CASE WHEN EXTRACT(MONTH FROM dateshipped)::int = 1  THEN 1 ELSE 0 END) AS Jan,
       SUM(CASE WHEN EXTRACT(MONTH FROM dateshipped)::int = 2  THEN 1 ELSE 0 END) AS Feb,
       SUM(CASE WHEN EXTRACT(MONTH FROM dateshipped)::int = 3  THEN 1 ELSE 0 END) AS Mar,
       SUM(CASE WHEN EXTRACT(MONTH FROM dateshipped)::int = 4  THEN 1 ELSE 0 END) AS Apr,
       SUM(CASE WHEN EXTRACT(MONTH FROM dateshipped)::int = 5  THEN 1 ELSE 0 END) AS May,
       SUM(CASE WHEN EXTRACT(MONTH FROM dateshipped)::int = 6  THEN 1 ELSE 0 END) AS Jun,
       SUM(CASE WHEN EXTRACT(MONTH FROM dateshipped)::int = 7  THEN 1 ELSE 0 END) AS Jul,
       SUM(CASE WHEN EXTRACT(MONTH FROM dateshipped)::int = 8  THEN 1 ELSE 0 END) AS Aug,
       SUM(CASE WHEN EXTRACT(MONTH FROM dateshipped)::int = 9  THEN 1 ELSE 0 END) AS Sep,
       SUM(CASE WHEN EXTRACT(MONTH FROM dateshipped)::int = 10 THEN 1 ELSE 0 END) AS Oct,
       SUM(CASE WHEN EXTRACT(MONTH FROM dateshipped)::int = 11 THEN 1 ELSE 0 END) AS Nov,
       SUM(CASE WHEN EXTRACT(MONTH FROM dateshipped)::int = 12 THEN 1 ELSE 0 END) AS Dec
FROM Shipments
WHERE EXTRACT(YEAR FROM dateshipped)::int=2016

Answer 2

自9.4起，您可以使用FILTER

SELECT
    count(*) AS total,
    count(*) FILTER (WHERE Extract(MONTH FROM dateshipped)::int=1) AS JAN,
    count(*) FILTER (WHERE Extract(MONTH FROM dateshipped)::int=2) AS FEB,
    ...
FROM Shipments
WHERE Extract(YEAR FROM dateshipped)::int=2016;

Answer 3

尝试使用sum函数：

Select 
   sum(case when extract(MONTH from dateshipped)=1 then 1 else 0 end) as jan,
   sum(case when extract(MONTH from dateshipped)=2 then 1 else 0 end) as feb,
   sum(case when extract(MONTH from dateshipped)=3 then 1 else 0 end) as march
   .....
   .....
from Shipments
Where EXTRACT(YEAR FROM dateshipped)::int=2016;

是否可以在一个查询中按不同条件计数？

3 个答案: