我有这个疑问：
SELECT
Count(*) as Cnt,
Category
FROM [MyDb].[dbo].[MyTable]
group by Category
order by Cnt
这让我在每个计算行的Category 。 现在，我想补充的第三列，这将使我Cnt / (total rows in this table) 。
我怎样才能做到这一点？
Answer 1:
你可以使用子查询做到这一点：
SELECT Count(*) as Cnt, Category,
(Cast(Count(*) as real) / cast((SELECT Count(*) FROM [MyDb].[dbo].[MyTable]) as real)) AS [Percentage]
FROM [MyDb].[dbo].[MyTable]
group by Category
order by Cnt
或具有可变：
declare @total real;
select @total = count(*) from [MyDb].[dbo].[MyTable];
SELECT Count(*) as Cnt, Category, (Cast(Count(*) as real) / @total) AS [Percentage]
FROM [MyDb].[dbo].[MyTable]
group by Category
order by Cnt
我已经投COUNT（*）作为真正在这两个例子中，以避免整数分型的问题。
希望这有助于约翰
Answer 2:
作为一个说明，你其实可以用一个查询使用窗口函数做到这一点：
SELECT Count(*) as Cnt, Category,
cast(Count(*) as float) / sum(count(*)) over () as ThirdColumn
FROM [MyDb].[dbo].[MyTable]
group by Category
order by Cnt
文章来源: SQL - percentage of total rows
