LINQ版本的SQL，具有左联接和分组依据

Question

谁能告诉我这个SQL的linq查询？

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

您的SQL查询的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) };

如果您有值（ID），在表1，但不是在表2（itemid的），那么t内grouped.Sum()将是空的，所以你需要检查是否t不是null t.price也不是里面空grouped.sum()

Answer 2

用作

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();