用where子句分隔SQL

Question

我需要划分，其中推銷員Yes和產品是Pen 超過銷售總額（在我的情況是8），並獲得總百分比。

select * from mytable   

Sale_Number      Date            Salesman_Used           Product

 1            01/01/2014             No                    Pen
 2            01/02/2014             No                    Pen
 3            01/03/2014             Yes                   Pen
 4            01/04/2014             Yes                   Pencil
 5            01/05/2014             Yes                   Pen
 6            01/06/2014             Yes                   Pencil  
 7            01/07/2014             No                    Pencil
 8            01/08/2014             No                    Pencil

我被卡在丟失的那一塊上：

select concat(100 * count(missing this piece) / count(Sale_Number), '%') 
as "Salesman Sales for Pens"
from mytable
where Salesman_Used = 'Yes' 
and Product = 'Pen'            

我嘗試的問題是where clause Sale_Number影響Sale_Number 。我該怎么做？ 提前致謝。

Answer 1

您可以使用子查詢來獲取銷售條目的總數：

select concat(100 * count(*) / (select count(*) from mytable), '%') 
as "Salesman Sales for Pens"
from mytable
where Salesman_Used = 'Yes' 
and Product = 'Pen'  

Answer 2

嘗試這個：

select concat(100 * count(missing this piece) / count(select Sale_Number from mytable), '%') 
as "Salesman Sales for Pens"
from mytable
where Salesman_Used = 'Yes' 
and Product = 'Pen' 

Answer 3

聚合有filter子句：

如果指定了FILTER，則只有filter_clause評估為true的輸入行才被饋送到聚合函數； 其他行將被丟棄。

所以：

select concat(100 * count(*) filter (where Salesman_Used = 'Yes' and Product = 'Pen') / count(Sale_Number), '%') 
as "Salesman Sales for Pens"
from mytable

Answer 4

我從沒用過Postgresql，但是也許可以用：

select concat(100 * (select count(*) from mytable) / count(Sale_Number), '%') 
as "Salesman Sales for Pens"
from mytable
where Salesman_Used = 'Yes' 
and Product = 'Pen'