linq中的join是inner join内连接,就是当两个表中有一个表对应的数据没有的时候那个关联就不成立。比如表A B的数据如下 ?...from a in A join b in B on a.BId equals b.Id select new {a.Id, b.Id} 的结果是 {1,1} {2,2} {4...
usr/local/share/dotnet/sdk"; var fileList = Directory.GetFiles(startFolder, "*.*", SearchOption.AllDirectories); var fileQuery = from file in fileList let fileLen = new FileInfo(file).Length where fileLen > 0 select fileLen; // Cache the results to avoid multiple trips to the...
9.多列(Multiple Columns) var categories = from p in db.Products group p by new { p.CategoryID, p.SupplierID } into g select new { g.Key, g }; 语句描述:Linq使用Group By按CategoryID和SupplierID将产品分组。 说明:既按产品的分类,又按供应商分类。在by后面,new出来一个匿名类。这里,Key其...
多列(Multiple Columns)#Copyvar categories = from p in db.Products group p by new { p.CategoryID, p.SupplierID } into g select new { g.Key, g }; 语句描述:使用Group By按CategoryID和SupplierID将产品分组。说明:既按产品的分类,又按供应商分类。在by后面,new出来一个匿名类。这里,Key其实质...
SELECT column aliases: Refer to alias in another column? SELECT COUNT from 2 intersected tables select count(*) Select DISTINCT in LEFT JOIN SELECT DISTINCT on one column, with multiple columns returned Select event where date >= today
3.多列(Multiple Columns)var dateQDList = from T in hisDZD group T by new { T.JiaoYiRQ, T.JiaoYiQDMC } into g select new { g.Key.JiaoYiRQ, g.Key.JiaoYiQDMC }; 语句描述:Linq使用Group By按交易日期和交易渠名称将his对账单进行分组统计。
(file).LengthwherefileLen >0selectfileLen;// Cache the results to avoid multiple trips to the file system.long[] fileLengths = fileQuery.ToArray();// Return the size of the largest filelonglargestFile = fileLengths.Max();// Return the total number of bytes in all the fil...
(file).LengthwherefileLen >0selectfileLen;// Cache the results to avoid multiple trips to the file system.long[] fileLengths = fileQuery.ToArray();// Return the size of the largest filelonglargestFile = fileLengths.Max();// Return the total number of bytes in all the files...
Retrieve related entity columns for 1 to N relationships Use .value to retrieve the value of an attribute Multiple projections, new data type casting to different types Use the GetAttributeValue method Use Math methods Use Multiple Select and Where clauses ...
具有别名的单个或多个属性。需要new。Select="new(Category As CategoryGroup)" 如果要启用自动数据修改,但不想显示数据对象中的所有属性,请不要设置Select属性。 而是通过数据绑定控件管理显示。 使用DetailsView控件或GridView控件时,还必须将AutoGenerateRows或AutoGenerateColumns属性设置为false。 未显示在数据绑定控件...