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最新推荐文章于 2025-05-14 11:43:56 发布

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最新推荐文章于 2025-05-14 11:43:56 发布

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文章标签： linq

本文链接：https://blog.youkuaiyun.com/m0_50623581/article/details/110469199

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博客涉及LINQ相关内容，但具体信息缺失。LINQ是信息技术领域后端开发中用于数据查询和操作的技术。

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分组求最大值
 var query = from a in tempData
			 group a by a.ssn into g
			 select new
			 {
			     ssn = g.Key,
			     shipdate = g.Max(x => x.shipdate)
			 };

//var query2 = tempData.GroupBy(x => x.ssn).Select(g => new { ssn = g.Key, shipdate = g.Max(s => s.shipdate) }).ToList();
左连接
var Result = from a in Lssn
             join b in query on a.ssn equals b.ssn into a_b
             from d in a_b.DefaultIfEmpty()
             orderby a.Order                              
             select new
             {
                 num = a.Order,
                 ssn = a.ssn,
                 //shipdate = d.shipdate
                 shipdate = d != null ? d.shipdate : null,                  
             };
//注意如果为空shipdate = d != null ? d.shipdate : null, 会报‘未将对象设置应用到实例’的错误
 /* select a.ssn,b.maxlastdate from aa_wangjp a left join
    (select b.ssn, max(b.lastdate) as maxlastdate from aa_wangjp_2 b group by b.ssn) 
    b on a.ssn = b.ssn order by a.orderr*/