大佬教程收集整理的这篇文章主要介绍了使用GROUP BY和COUNT(DISTINCT)的LINQ to SQL,大佬教程大佬觉得挺不错的,现在分享给大家,也给大家做个参考。
尚无直接支持COUNT(disTinCT {x}))
,但您可以从IGrouPing<,>
(即group by
返回什么)中进行模拟。恐怕我只“做”
C#,所以您必须转换为VB。
SELEct new
{
Foo= grp.Key,
bar= grp.SELEct(x => x.someFIEld).disTinct().Count()
};
这是罗斯文(northwind)的示例:
using(var ctx = new DataClasses1DataContext())
{
ctx.Log = Console.out; // log Tsql to console
var qry = from cust in ctx.Customers
where cust.CustomerID != ""
group cust by cust.Country
into grp
SELEct new
{
Country = grp.Key,
Count = grp.SELEct(x => x.City).disTinct().Count()
};
foreach(var row in qry.orderBy(x=>x.Country))
{
Console.Writeline("{0}: {1}", row.Country, row.Count);
}
}
Tsql不是我们想要的,但是可以完成工作:
SELECT [t1].[Country], (
SELECT COUNT(*)
FROM (
SELECT disTinCT [t2].[City]
FROM [dbo].[Customers] AS [t2]
WHERE ((([t1].[Country] IS NulL) AND ([t2].[Country] IS NulL)) OR (([t1]
.[Country] IS NOT NulL) AND ([t2].[Country] IS NOT NulL) AND ([t1].[Country] = [
t2].[Country]))) AND ([t2].[CustomerID] <> @p0)
) AS [t3]
) AS [Count]
FROM (
SELECT [t0].[Country]
FROM [dbo].[Customers] AS [t0]
WHERE [t0].[CustomerID] <> @p0
GROUP BY [t0].[Country]
) AS [t1]
-- @p0: input NVarChar (Size = 0; Prec = 0; Scale = 0) []
-- Context: sqlProvIDer(sql2008) Model: Attributedmetamodel Build: 3.5.30729.1
但是,通过手动运行结果可以正确验证:
const @R_197_3637@ = @"
SELECT c.Country, COUNT(disTinCT c.City) AS [Count]
FROM Customers c
WHERE c.CustomerID != ''
GROUP BY c.Country
ORDER BY c.Country";
var qry2 = ctx.Executequery<queryResult>(sql);
foreach(var row in qry2)
{
Console.Writeline("{0}: {1}", row.Country, row.Count);
}
具有定义:
class queryResult
{
public String Country { get; set; }
public int count { get; set; }
}
我必须执行以下SQL查询:
SELEct answer_nbr,count(disTinct user_nbr)
from tpoll_answer
where poll_nbr = 16
group by answer_nbr
LINQ to SQL查询
from a in tpoll_answer
where a.poll_nbr = 16 SELEct a.answer_nbr,a.user_nbr disTinct
映射到以下SQL查询:
SELEct disTinct answer_nbr,disTinct user_nbr
from tpoll_answer
where poll_nbr = 16
到目前为止,一切都很好。但是,在尝试对结果进行分组时会出现问题,因为我无法找到映射到我在此处编写的第一个查询的LINQ to
SQL查询(感谢LINQPad,使此过程更加容易)。以下是我发现的唯一给我期望结果的结果:
from answer in tpoll_answer where answer.poll_nbr = 16 _
group by a_id = answer.answer_nbr into votes = count(answer.user_nbr)
依次在所有SQL查询中产生以下丑陋且未优化的结果:
SELECT [t1].[answer_nbr] AS [a_id],(
SELECT COUNT(*)
FROM (
SELECT CONVERT(Bit,[t2].[user_nbr]) AS [value],[t2].[answer_nbr],[t2].[poll_nbr]
FROM [TPOLL_ANSWER] AS [t2]
) AS [t3]
WHERE ([t3].[value] = 1) AND ([t1].[answer_nbr] = [t3].[answer_nbr]) AND ([t3].[poll_nbr] = @p0)
) AS [votes]
FROM (
SELECT [t0].[answer_nbr]
FROM [TPOLL_ANSWER] AS [t0]
WHERE [t0].[poll_nbr] = @p0
GROUP BY [t0].[answer_nbr]
) AS [t1]
-- @p0: Input Int (Size = 0; Prec = 0; Scale = 0) [16]
-- Context: SqlProvider(Sql2008) Model: AttributedMetaModel Build: 3.5.30729.1
任何帮助将不胜感激。
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