------解决方案--------------------
var query= from t1 in ds1["mytab"].AsEnumerable() join t2 in ds2["mytab"].AsEnumerable() on t1.Field<int>("编号") equals t2.Field<int>("编号") into t from t2 in t.DefaultIfEmpty() select new { 编号=t1.Field<int>("编号") , 姓名=t2==null?"":t2.Field<string>("姓名") , // 后边自己添加 };