LINQ版本的SQL與左連接和組由

Question

任何人都可以告訴我這個SQL的LINQ查詢？

select 
    t1.item, 
    IsNull(sum(t2.price), 0) total 
from table1 t1 
left join table2 t2 
    on t1.id = t2.itemid 
group by t1.item 

Answer 1

使用它作爲

var result = (from t1 in table1 
         join t2 in table2 on t1.id equals t2.itemId 
        into t2d from td in t2d.DefaultIfEmpty() 
        group t1 by t1.item into t1g select new {item=t1g.key, sum =t1g.Sum(p=>p.price??0)}).ToList(); 

Answer 2

您的SQL查詢的LINQ版本，

var resutl = from t1 in objtable1 
        join t2 in objtable2 on t1.id equals t2.itemid into j1 
        from j2 in j1.DefaultIfEmpty() 
        group j2 by t1.item into grouped 
        select new { item = grouped.Key, sum = grouped.Sum(t => t != null ? (t.price ??0) : 0) }; 

如果你在表1的值（ID），而不是在表2（itemid的），然後t內grouped.Sum()將是空的，所以你需要檢查t不是null t.price也不是空內grouped.sum()