利用 c# linq 实现跨数据库的联合查询

string sql = "select * from V_LoginLog where denglurq=@RQ";
DataTable dt = MsSqlHelper.ExecuteDataTable(ConnUeHis, sql, new SqlParameter("@RQ", rq));
string sql1 = "select * from  app_getopdschdule where OPDDATE=:OPDDATE";
DataTable dt1 = OracleHelper.ExecuteDataTable(ConnStrLzHis, sql1, new OracleParameter(":OPDDATE", rq));
var res = from m in dt.AsEnumerable()
          from s in dt1.AsEnumerable()
          where m.Field<string>("LoginUser") == s.Field<string>("DOCTORID") && m.Field<string>("shangxiawbz") == Convert.ToString(s.Field<decimal>("OPDTIMEID"))
          select new
          {
             DoctorName = s.Field<String>("DOCTORNAME"),
             OpdTimeID = m.Field<String>("shangxiawbz"),
             LoginTime = m.Field<DateTime>("denglusj"),
             RoomName = s.Field<String>("ROOMNAME")
          };
DataTable DtTemp = new DataTable();
DtTemp.Columns.Add("DoctorName", typeof(String));
DtTemp.Columns.Add("OpdTimeID", typeof(String));
DtTemp.Columns.Add("RoomName", typeof(String));
DtTemp.Columns.Add("LoginTime", typeof(String));
foreach (var obj in res)
{
     DtTemp.Rows.Add(obj.DoctorName, obj.OpdTimeID == "1" ? "上午" : "下午", obj.RoomName, obj.LoginTime.ToString("yyyy-MM-dd HH:mm:ss"));

}
return CommonHelper.Dtb2Json(DtAll);