Depending on items, stats, abilities, and types, most attacks will do 1 damage to the opponent at the least. Unless if the Aggron was holding an item or has a certain ability, the Rattata should do at least 1 damage. Also, if the Rattata's move type move does not affect Aggron's type, then there will not be any damage done. Another thing, the Aggron's speed stat should be higher than the Rattata's as of Aggron being level 100 and Rattata being level 1, causing Aggron to attack first. If Aggron uses a move that can in some way damage Rattata, then Rattata will most likely faint because the Aggron's attack stat is so high and the Rattata's defense stat is so low. So, if Rattata faints, then it wouldn't have gotten the chance to attack, therefore causing Rattata not to do any damage to Aggron.