linq - 加入 groupby 后的 linq 并选择

Question

我需要在常规 sql 查询命令中构造一个这样的 linq：

select t1.vendorcode, t1.location, sum(t1.sales)
from table1 t1
where t1(vendorCode, location) in
      (select t2.vendorCode, t2.location from table2 t2) 
groupby t1.vendorCode, t1.location

我构造linq如下：

query = from t1 in table1
where ...
join t2 in table2 on new
{
  t2.vendorcode, t2.location
} equals new
{ 
  t1.vendorcode, t1.location 
}

我的问题是：我应该如何构建这个 linq？我需要另一个子查询还是可以添加更多group by并选择语句来完成这个 linq？

Answer 1

您不需要添加另一个group by子句 - 您只需要选择总和：

var query = from t1 in table1
            join t2 in table2 
              on new { t1.vendorcode, t1.location } equals
                 new { t2.vendorcode, t2.location }
            group t1 by new { t1.vendorcode, t1.location } into g
            select new { 
                g.Key.vendorcode,
                g.Key.location, 
                g.Sum(t1 => t1.sale)
            };

如果table2任何特定的供应商代码/位置对中只有一条记录，这将起作用。但是，如果可以有多个这样的记录，那么它就不起作用 - 你可能想要更多类似的东西：

var query = from t1 in table1
            where table2.Select(t2 => new { t2.vendorcode, t2.location })
                        .Contains(new { t1.vendorcode, t1.location })
            group t1 by new { t1.vendorcode, t1.location } into g
            select new { 
                g.Key.vendorcode,
                g.Key.location, 
                g.Sum(t1 => t1.sale)
            };

从逻辑上讲，这就是您的“存在”版本。

Answer 2

这应该这样做

var query =
    from t1 in table1

    join t2 in table2
    on new { vc = t1.vendorcode, lc = t1.location }
    equals new { vc = t2.vendorcode, lc = t2.location }

    group t1 by new { vc = t1.vendorcode, lc = t1.location };