In Data Explorer, looking through some SO data, I noticed that some comments have 0 for Score, while others are null. Why is this? Is there a difference between 0 and null comment scores?
Similar to the answer given here by Catija, Comments that received an upvote that was later retracted have a Score of 0, whereas Comments that never received any upvotes are inserted into the table with a Score of NULL.
Also similar to favorites (even less useful, I'd argue), not much can be read into this information, as someone could've upvoted by accident and then simply removed it right after, or changed their mind about the upvote for any reason.
Especially considering that the timeframe you have to remove upvotes is small.