两个表Table1、Table2 并表查下时，如果连接字段存在空值，直接用join 查不出数据，需用左连接
var list = from v in Table1
join x in Table2 on v.Id equals x.Table1Id into newlist
from d in newlist.DefaultIfEmpty()
原文：https://www.cnblogs.com/qingheshiguang/p/13367482.html