EF 左联合

  var q1 = db.IntelligenceTable.Where(x => x.IsUsable == 0).GroupJoin(db.Users, x => x.Publisher, y => y.id,
                (x, y) => new { x, PName = y.FirstOrDefault().Name }).GroupJoin(db.Users, x => x.x.Auditor, y => y.id,
                (x, y) => new { x.x.id, x.x.Contents, x.PName, AName = y.FirstOrDefault().Name }).ToList();

   var q2 = (from i in db.IntelligenceTable
                      join pu in db.Users on i.Publisher equals pu.id into pui
                      from pu in pui.DefaultIfEmpty()
                      join pa in db.Users on i.Auditor equals pa.id into pai
                      from pa in pai.DefaultIfEmpty()
                      select new
                      {
                          i.id,
                          i.Contents,
                          Pn = pu.Name,
                          Pa = pa.Name
                      }).ToList();