C# 从元组获取结果的快速查询
我有一个表格记录了两个有效的英国邮政编码与Google/Bing之间的距离。在使用系统时,会将此表添加到中,以便下一个距离查询变得快速,并且我不必调用web服务在线检索距离 以下是表格结构:C# 从元组获取结果的快速查询,c#,sql-server-2008,linq-to-sql,gis,C#,Sql Server 2008,Linq To Sql,Gis,我有一个表格记录了两个有效的英国邮政编码与Google/Bing之间的距离。在使用系统时,会将此表添加到中,以便下一个距离查询变得快速,并且我不必调用web服务在线检索距离 以下是表格结构: OID PostcodeA PostcodeB DistanceMeters DistanceMiles -------------------- --------- --------- ----------
OID PostcodeA PostcodeB DistanceMeters DistanceMiles
-------------------- --------- --------- --------------------------------------- ---------------------------------------
1 BR60PS BT248DN 788847 490
2 BR60PS CM201JA 64426 40
3 BR60PS CM82AP 77640 48
4 BR60PS CO123AX 131617 82
5 BR60PS CT146EL 119366 74
6 BR60PS DA110TA 29247 18
7 BR60PS DE216AH 262570 163
8 BR60PS DL81AB 397524 247
9 BR60PS HG27JE 368802 229
10 BR60PS IP121AL 144394 90
11 BR60PS IP141AH 144183 90
12 BR60PS IP209AH 172259 107
现在我有了一个标量UDF,我通过Linq to SQL使用它,它的定义如下:
ALTER FUNCTION [dbo].[GetDistanceFromCache]
(@PostcodeA VARCHAR (MAX), @PostcodeB VARCHAR (MAX))
RETURNS DECIMAL
AS
BEGIN
DECLARE @FoundDistance AS DECIMAL;
SELECT @FoundDistance = DistanceMiles
FROM AddressInfoRecordedDistance
WHERE (PostcodeA = @PostcodeA
AND PostcodeB = @PostcodeB)
OR (PostcodeB = @PostcodeA
AND PostcodeA = @PostcodeB);
RETURN ISNULL(@FoundDistance, -1);
END
我需要知道是否有更快的SQL语句或c linq来获得结果?如果我检索800名员工并对50个作业运行他们,系统将进入暂停状态,如果我不将DBContext.GetDistanceFromCache添加到选择集,所花费的时间将大大减少
下面是暂停查询:
var query =
from locum in DbContext.Locums
where
locum.IsActive == true &&
locum.IsAdminMarkedComplete == true &&
locum.IsLocumsExciteBan == false &&
locum.IsGPHCBan == false &&
filterID1.Contains(locum.OID) == false &&
filterID2.Contains(locum.OID) == false
select new {
LocumID = locum.OID,
LocumName = locum.FirstName + " " + locum.LastName,
locum.MobileNumber,
locum.Email,
Gender = locum.Gender ? "Male" : "Female",
locum.DateofBirth,
LocumType = locum.LocumType.Name,
**Distance** = DbContext.GetDistanceFromCache(_Postcode, locum.AddressInfo.Postcode),
Address = String.Format("{0} {1} {2} {3}",
locum.AddressInfo.House.Length == 0 ? String.Empty : locum.AddressInfo.House + ", ",
locum.AddressInfo.Street.Length == 0 ? String.Empty : locum.AddressInfo.Street + ", ",
locum.AddressInfo.Area.Length == 0 ? String.Empty : locum.AddressInfo.Area + ", ",
locum.AddressInfo.Postcode ?? String.Empty),
Postcode = locum.AddressInfo.Postcode,
City = locum.AddressInfo.City.Name,
County = locum.AddressInfo.City.County.Name,
locum.SystemUserID
};
我认为您的查询很慢,因为每次LINQ查询选择new{…}时都必须调用DB,这与您有结果行的次数相同 在将结果集与之匹配之前,我将从表AddressInforecordAddInstance下载数据。我是这样想的:
var query = from locum in DbContext.Locums
where ...
select new { ... }; // Don't include GetDistanceFromCache here
var airds = from a in DbContext.AddressInfoRecordedDistance
select a;
foreach (var q in query)
q.Distance = GetDistanceFromCache(q.PostcodeA, q.PostcodeB, airds);
就在这里。当然,您还需要GetDistanceFromCache方法:
当然,如果您多次运行上述所有操作,您应该缓存变量airds。如果您对距离查询的脏读取感到满意,您可以添加表提示,如Nolock。有关更多信息,请参阅
另一个选项是确保在AddressInRecordedDatabase表上为PostcodeA和PostcodeB设置了适当的索引,并且变量和字段的数据类型匹配,因此没有隐式数据类型转换。创建索引是一个非常有价值的建议。让我们看看我是否能在这里获得一些速度。我确实获得了速度。我还通过在PostcoseA和PostcodeB列上添加唯一的约束来确保数据的一致性。
// The SQL UDF in C# code here (psuedo code, not tested, just "C blunt")
decimal GetDistanceFromCache(string PostcodeA, string PostcodeB, List<...> table)
{
return (from t in table
where
(t.PostcodeA == PostcodeA && t.PostcodeB == PostcodeB) ||
(t.PostcodeB == PostcodeA && t.PostcodeA == PostcodeB)
select t).FirstOrDefault().DistanceMiles;
}