在SQL查詢中，我可以對不同的結果列使用不同的where子句嗎？

Question

一個人爲的例子：說我有一個簡單的表格，有2列 - 日期和（數字）ID。我想知道，每一天，甚至有多少比例的ID。

我可以在2個查詢做到這一點：

查詢＃1：

select date, id % 2, count(*) 
from my_table 
group by date, id % 2 
order by date, id % 2 

查詢＃2：

select date, count(*) 
from my_table 
group by date 
order by date 

然後我手動（即，在電子表格）排隊列和做數學。

這當然很麻煩 - 有沒有辦法在一個查詢中做到這一點？

喜歡的東西：

select 
    date, 
    [count where id % 2 = 0], [total count], 
    [count where id % 2 = 0/total count] 
from my_table 
group by date 
order by date 

Answer 1

使用條件sum()

select date, 
     sum(case when id % 2 = 0 then 1 else 0 end) * 100/count(*) as evenPercentage, 
     sum(case when id % 2 = 1 then 1 else 0 end) * 100/count(*) as unevenPercentage, 
     count(*) as totalCount, 
     sum(case when id % 2 = 0 then 1 else 0 end) as evenCount, 
     sum(case when id % 2 = 1 then 1 else 0 end) as unevenCount 
from my_table 
group by date 
order by date