# My professor claims that inserting the same key into a hash table again will lead to a collision … – Is he really right?

My whole life I thought

a collision is a situation that occurs when two distinct pieces of data have the same hash value.

Everything looks a little bit different now: A few days ago we had to analyse common collision resolution strategies to handle the event that at least two keys being hashed to the same slot of an ordinary hash table. As mentioned above, to my knowledge (as well as my intuition) when inserting the very same key $$k$$ – that is already assigned to a slot of a hash table $$T$$ – again, nothing (special) happens and $$T$$ remains unchanged.

I wonder now, if i misunderstood this basic concept, since my professor claims, that inserting the key $$k$$ into a hash table $$T$$ again will lead to a collision anyway and we have to analyse some collision resolution strategies in this case too …