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