如何在SQL Server Compact Edition中进行此查询？

Question

此子查询在SQL Server中有效:

select systemUsers.name, 
    (select count(id) 
     from userIncidences 
     where idUser = systemUsers.id ) 
from systemUsers

如何在SQL Compact中创建？

谢谢!

Answer 1

有些情况下,您无法避免子查询,例如,如果您必须包含使用当前行和上一行数据的计算列.考虑这个查询,例如:

SELECT     
     (Current.Mileage - Last.Mileage)/Quantity as MPG
FROM         
     GasPurchases AS Current
     LEFT OUTER JOIN GasPurchases AS Last
     ON Last.Date =
        (SELECT MAX(PurchaseDate)
        FROM GasPurchases
        WHERE PurchaseDate < Current.PurchaseDate)

它会导致解析错误:

SQL执行错误.

错误源:SQL Server Compact ADO.NET数据提供程序错误消息:解析查询时出错.

我在MSDN上找到了这个有解决方法的线程.通过更改子查询以便它返回一个集而不是标量值,我能够保存并运行以下查询.

SELECT     
     (Current.Mileage - Last.Mileage)/Quantity as MPG
FROM         
     GasPurchases AS Current
     LEFT OUTER JOIN GasPurchases AS Last
     ON Last.Date IN
        (SELECT MAX(PurchaseDate)
        FROM GasPurchases
        WHERE PurchaseDate < Current.PurchaseDate)

Answer 2

试试这个:

SELECT su.Name, COUNT(ui.ID)
FROM systemUsers su
LEFT JOIN userIncidences ui ON ui.idUser = su.ID
GROUP BY su.Name

[编辑:]
我最初有一个像Tomalak一样的INNER JOIN,但我意识到这会排除没有事件的用户,而不是用0计数显示它们.这甚至可能是你想要的,但它与你原来的不符.