EF+Lambda 拼接Join+GroupBy+Select+

            var query = _bussubsidyRepository.GetAll().
            Join(_instanceRepository.GetAll(), i => i.a.ToString(), j => j.id.ToString(), (i, j) => new { i, j }).DefaultIfEmpty();

              query= await query
               .GroupBy(e => new { e.i.a})
               .Select(e => (new
               {
                   a= e.i.a,
                   b= e.Max(m => m.i.b),
                   c= e.Sum(m => m.i.c)
               }))
                .OrderByDescending(e => e.i.a)
                .PageBy(input)
                .ToListAsync();

Join:表连接
GroupBy:分组
Select:显示列
OrderByDescending:排序
PageBy:分页
ToListAsync:转换为List型