sort when you go from SD99999 to SD100000

How do you sort when the number exceedes? 

Now SD99999 is coming after SD100000 because it is a char and it will se SD100000 as the lower number then SD99999 -> anyone faced this issue? 

I found a KM that says you could sort on open.time but that could influence performance. 

Any other ideas? 


BR Ivis.