EFCore中 join on的不同

当 多条件 left join on 时

left outer join

on new { u.userid, ue.examid } equals new { sac.userid, sac.examid }
into sac2
from sac in sac2.defaultifempty()

生成sql 为 

 on ([filter1].[userid1] = [groupby1].[k1]) and (([filter1].[examid2] = [groupby1].[k2]) or (([filter1].[examid2] is null) and ([groupby1].[k2] is null)))

单条件 on 时 

sql on 没有空值判断

  left outer join [dbo].[sysquestion] as [extent3] on [groupby1].[k1] = [extent3].[queid]