總銷售額和按月購買相同記錄組？

Question

我有一個這樣的桌子。

id date  subtotal type 
1 |2017-12-12 | 50.00 | 1 
2 |2017-12-12 | 20.00 | 2 
3 |2017-11-12 | 30.00 | 2 
4 |2017-11-12 | 40.00 | 1 
5 |2017-10-12 | 70.00 | 1 
6 |2017-10-12 | 250.00| 2 

在這種情況下，類型列顯示銷售（1）和購買（2）。我想要做的是，按月按此訂單分組，並在本月獲得總銷售額和購買量。像這樣的東西。

id date  sale  buy 
1 |December | 50.00 | 20.00 
2 |November | 30.00 | 40.00 
3 |October | 70.00 | 250.00 

當我嘗試這樣的事情，

select to_char(date,'Mon') as Month, 
     extract(year from date) as Year, 
     case when type= 1 then sum("subtotal") END as sales, 
     case when type= 2 then sum("subtotal") END as buys 
    from table 
    group by 1,2,type 

結果並不像我所希望的。這幾個月將出現在不同的列。喜歡這個。

month year sales buys 
Oct |2017| 70.00 | 0 
Oct |2017| 0  | 250.00 

我該如何做到這一點？我只想每月總結記錄。

Answer 1

你想有條件聚集：

select to_char(date,'Mon') as Month, 
     extract(year from date) as Year, 
     sum(case when type = 1 then subtotal else 0 end) as sales, 
     sum(case when type = 2 then subtotal else 0 end) as buys 
from table 
group by Month, Year; 

我經常發現它方便地在這種情況下使用date_trunc() ：

select date_trunc('month', date) as month_start, 
     sum(case when type = 1 then subtotal else 0 end) as sales, 
     sum(case when type = 2 then subtotal else 0 end) as buys 
from table 
group by month_start 
order by month_start; 

Answer 2

在您的查詢中，您也按年份分組，這就是爲什麼它將所有內容合計在同一行中。 這應該給你想要的東西：

select to_char(date,'Mon') as Month, 
     extract(year from date) as Year, 
     case when type= 1 then sum("subtotal") END as sales, 
     case when type= 2 then sum("subtotal") END as buys 
    from table 
    group by 1 

Answer 3

你可以試試這個

Select a.Month,a.Year,sum(a.sales) sales,sum(a.buys) buys 
from ( 
    select convert(char(3),date, 0) as Month, 
     year(date) as Year, 
     isnull(case when type= 1 then sum(subtotal) END,0) as sales, 
     isnull(case when type= 2 then sum(subtotal) END,0) as buys  
    from _table  
    group by convert(char(3),date, 0),year(date),type 
) a 
group by a.Month,a.Year