Question

这是我的sql命令：

select 
    b.Brand, 
    count(b.Brand) as BrandCount,
    SUM(a.Qty) as DeviceCount 
from (
    select * from DeviceList
) as a 
join DeviceMaster as b 
    on a.DeviceMasterId = b.Id
group by b.Brand

这是我到目前为止所尝试的内容：

var v1 = (from p in ghostEntities.DeviceMasters 
          join c in ghostEntities.DeviceLists on p.Id equals c.DeviceMasterId 
          select new table_Model { 
            Id = c.Id, 
            qty = c.Qty.Value, 
            month = c.DMonth, 
            brand = p.Brand, 
            model = p.Model, 
            memory = p.Memory
          }).ToList();

我从两个表中获取值，但不能对它们进行分组或添加值。

Answer 1

您应该在您的LINQ查询中添加group by并使用Distinct（）。Count（）和Sum（）聚合函数：

var query = from a in ghostEntities.DeviceList
   join b in ghostEntities.DeviceMaster on a.DeviceMasterId equals b.Id
   group b by b.Brand into g
   select new { g.Key, count =g.Select(x => x.Brand).Distinct().Count(), sum = g.Sum(x => x.Qty) };

你可以在https://code.msdn.microsoft.com/101-LINQ-Samples-3fb9811b找到很多LINQ样本，我希望它能为你提供帮助。

Answer 2

按表格分组后，会失去对联接操作中其他表格字段的访问权限，可能的解决方法是：

var results = (from a in DeviceList
                join b in DeviceMaster
                on a.DeviceMasterId equals b.Id
                group new { a, b } by new { b.Brand } into grp
                select new
                {
                    Brand = grp.Key.Brand,
                    BrandCount = grp.Count(),
                    DeviceCount = grp.Sum(x=> x.a.Qty.GetValueOrDefault())
                }).ToList();

我需要将sql转换为Linq

2 个答案: