Question

我在SQL Server Management Studio 2012中的简单查询如下： -

SELECT Last_Name, City,
(SELECT COUNT (City) FROM Customers IX WHERE IX.City = EX.City) as counting
FROM Customers EX
GROUP BY City, Last_Name
ORDER BY City

输出： -

Last_Name   City    Counting
Joe     London  3
Smith   London  3
Carter  London  3
Stones  New York    3
Jones   New York    3
White   New York    3

但我希望它不要重复同一个城市的计数和输出如下： -

Last_Name   City    Counting
Joe     London  3
Smith   London  
Carter  London  
Stones  New York    3
Jones   New York    
White   New York

我将如何实现这一目标？

Answer 1

看起来像一个非常奇怪的请求，并且很容易在应用程序端完成。但是在SQL中并不难：

SELECT Last_Name, City,
       (case when row_number() over (partition by Last_Name, City order by (select NULL)) = 1
             then (SELECT COUNT(City) FROM Customers IX WHERE IX.City = EX.City) as counting
        end) as Counting
FROM Customers EX
GROUP BY City, Last_Name
ORDER BY City;

这会将值放在每个城市的一行上。它不是确定哪一个，但可能是实践中的第一个。您可以通过使用稳定的排序来保证这一点：

SELECT Last_Name, City,
       (case when row_number() over (partition by Last_Name, City order by Last_Name) = 1
             then (SELECT COUNT(City) FROM Customers IX WHERE IX.City = EX.City) as counting
        end) as Counting
FROM Customers EX
GROUP BY City, Last_Name
ORDER BY City, Last_Name

SQL COUNT只显示一次结果

1 个答案: