increase row in database

in the database I have some number, like: 1, 2, 3, 999,999 - from above to down

 but if you want to sort up, then if 999 is above the last number not 999 then number has to be number + 1, so in this case 3 became 4, but if you have 4 it will be 5

 do you have maybe something for it

 if (medicijn.Volgorde == 999)

{

//medicijn.Volgorde = ( 999 - medicijn.Volgorde) + 1;

medicijn.Volgorde = medicijn.Volgorde;

}