具有多个组的LINQ查询

Question

我以list的形式获得输出，如图所示。

此处month是一个字符串，year是一个整数。

Answer 1

我假设左图中的表是input表：

var result = from i in input
             groupby new { i.Company, i.Year, i.Month } into g
             select new {
                 g.Key.Company,
                 g.Key.Year,
                 g.Key.Month,
                 Version = g.Select(x => x.Version).Last()
             };

Answer 2

假设您的表名是 CompanyInfo ，那么

SQL Qyery：

select 
    Company,
    Year,
    Month, 
    Max(ActiveVersion) as ActiveVersion 
from 
    CompanyInfo 
Group by 
    Company, 
    Year, 
    Month

LINQ查询：

var result = from comp in CompanyInfo
                    group comp by new { comp.Company, comp.Year, comp.Month } into grp
                    select new {
                             grp.Key.Company,
                             grp.Key.Year,
                             grp.Key.Month,
                             Version = grp.Max(a => a.ActiveVersion)};

使用Lambda Expression：

var result = infos.GroupBy(grp => new { grp.Company, grp.Year, grp.Month })
            .Select(t => new CompanyInfo()
                {
                    Company = t.Key.Company,
                    Year = t.Key.Year,
                    Month = t.Key.Month,
                    ActiveVersion = t.Max(v => v.ActiveVersion)
                }).ToList();

Answer 3

        List<Record> list = new List<Record>();
        list.Add(new Record("ABC", 2014, "Jan", 1));
        list.Add(new Record("ABC", 2014, "Jan", 2));
        list.Add(new Record("ABC", 2014, "Jan", 3));
        list.Add(new Record("ABC", 2014, "Feb", 1));
        list.Add(new Record("ABC", 2014, "Feb", 2));
        list.Add(new Record("ABC", 2014, "Mar", 1));
        list.Add(new Record("ABC", 2014, "Mar", 2));
        list.Add(new Record("ABC", 2014, "Mar", 3));
        list.Add(new Record("ABC", 2014, "Apr", 1));
        list.Add(new Record("ABC", 2015, "Jan", 1));
        list.Add(new Record("ABC", 2015, "Jan", 2));
        list.Add(new Record("ABC", 2015, "Feb", 1));
        list.Add(new Record("ABC", 2015, "Mar", 1));
        list.Add(new Record("ABC", 2015, "Apr", 1));

        var result =  from record in list
                      group record by new { record.Company, record.Year, record.Month } into g
                         select new {
                             g.Key.Company,
                             g.Key.Year,
                             g.Key.Month,
                             Version = g.Count()};