sql - SQL - 总行数的百分比

Question

我有这个查询：

SELECT 
Count(*) as Cnt, 
Category
FROM [MyDb].[dbo].[MyTable]
group by Category
order by Cnt

它给了我每行的计数Category。现在我想添加第三列，它会给我Cnt / (total rows in this table).

我怎样才能做到这一点？

Answer 1

请注意，您实际上可以使用窗口函数通过一个查询来执行此操作：

SELECT Count(*) as Cnt, Category,
       cast(Count(*) as float) / sum(count(*)) over () as ThirdColumn
FROM [MyDb].[dbo].[MyTable]
group by Category
order by Cnt

Answer 2

你可以用一个子查询来做到这一点：

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

或使用变量：

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

在这两个示例中，我都将 count(*) 强制转换为实数，以避免整数除法类型问题。

希望这可以帮助约翰