? 前言
本示例主要实现 LINQ 查询，先分组，再聚合，最后在排序。示例很简单，但是使用 LINQ 却生成了不同的 SQL 实现。
1) 采用手动编写 SQL 实现
SELECT ROW_NUMBER() OVER(ORDER BY T.RealTotal DESC) AS SN, * FROM
(
SELECT (SELECT TradeName FROM UserInfo AS T2 WHERE T2.Id=T1.UserId) AS TradeName, (SELECT UserName FROM UserInfo AS T2 WHERE T2.Id=T1.UserId) AS UserName, SUM(T1.RealTotal) AS RealTotal FROM Orders AS T1
WHERE 1=1 AND T1.SalesUserId=131 AND T1.PayStatusId=2
AND (T1.PayTime>=‘2017-05-01 00:00:00‘ AND T1.PayTime<=‘2017-05-31 23:59:59‘)
GROUP BY T1.UserId
) AS T
2) LINQ 实现
var query = (from t1 in DataContext.Orders
where t1.SalesUserId == salesUserId && (t1.PayTime >= mbdt && t1.PayTime <= medt)
group t1 by t1.UserId into g1
select new
{
TradeName = (from t2 in DataContext.UserInfo
where t2.id == g1.Key
select t2.TradeName).FirstOrDefault(),
UserName = (from t2 in DataContext.UserInfo
where t2.id == g1.Key
select t2.userName).FirstOrDefault(),
RealTotal = g1.Sum(o => o.RealTotal)
}
into v1
orderby v1.RealTotal descending
select v1).AsEnumerable().Select((o, i) =>
new CustomOrderAmountRankingModel
{
Sn = i + 1,
CustomerShopName = o.TradeName,
RegisterUserName = o.UserName,
OrderAmount = o.RealTotal
});
3) 生成SQL
exec sp_executesql N‘SELECT
[Project10].[C1] AS [C1],
[Project10].[C2] AS [C2],
[Project10].[C3] AS [C3],
[Project10].[C4] AS [C4]
FROM ( SELECT
1 AS [C1],
[Project9].[C1] AS [C2],
[Project9].[C2] AS [C3],
[Project9].[C3] AS [C4]
FROM ( SELECT
[Project8].[C1] AS [C1],
[Project8].[C2] AS [C2],
(SELECT
SUM([Extent4].[RealTotal]) AS [A1]
FROM [dbo].[Orders] AS [Extent4]
WHERE ([Extent4].[SalesUserId] = @p__linq__0) AND ([Extent4].[PayTime] >= @p__linq__1) AND ([Extent4].[PayTime] <= @p__linq__2) AND ([Project8].[UserId] = [Extent4].[UserId])) AS [C3]
FROM ( SELECT
[Project7].[UserId] AS [UserId],
[Project7].[C1] AS [C1],
[Project7].[C2] AS [C2]
FROM ( SELECT
[Project5].[UserId] AS [UserId],
[Project5].[C1] AS [C1],
(SELECT TOP (1)
[Extent3].[userName] AS [userName]
FROM [dbo].[UserInfo] AS [Extent3]
WHERE [Extent3].[id] = [Project5].[UserId]) AS [C2]
FROM ( SELECT
[Project4].[UserId] AS [UserId],
[Project4].[C1] AS [C1]
FROM ( SELECT
[Project2].[UserId] AS [UserId],
(SELECT TOP (1)
[Extent2].[TradeName] AS [TradeName]
FROM [dbo].[UserInfo] AS [Extent2]
WHERE [Extent2].[id] = [Project2].[UserId]) AS [C1]
FROM ( SELECT
[Distinct1].[UserId] AS [UserId]
FROM ( SELECT DISTINCT
[Extent1].[UserId] AS [UserId]
FROM [dbo].[Orders] AS [Extent1]
WHERE ([Extent1].[SalesUserId] = @p__linq__0) AND ([Extent1].[PayTime] >= @p__linq__1) AND ([Extent1].[PayTime] <= @p__linq__2)
) AS [Distinct1]
) AS [Project2]
) AS [Project4]
) AS [Project5]
) AS [Project7]
) AS [Project8]
) AS [Project9]
) AS [Project10]
ORDER BY [Project10].[C4] DESC‘,N‘@p__linq__0 bigint,@p__linq__1 datetime2(7),@p__linq__2 datetime2(7)‘,@p__linq__0=131,@p__linq__1=‘2017-05-01 00:00:00‘,@p__linq__2=‘2017-05-31 23:59:59‘
4) 结果集（两种实现方式相同）
? 总结：可以看出 LINQ 生成的查询语句中，在子查询中使用 WHERE + DICTINCT 实现，并没有GROUP BY。两者执行耗时也没有什么区别，只是 LINQ 使用了过多的派生表，增加了理解的难度性。