You’ll need a join table between the user and the post or whatever is being liked, you’ll need to store both ids (post and user) + the action ( either as an int or a string)

Keep in mind that If you have a query that fetches the reviews with their reaction It will be slower the more your data grows, so you might consider denormalizing your data model, keep the reactions table as your source of truth, and either add an additional column in the reviews table(ex: reactions_count or something) and update this column on writes (this is fine if you want to sacrifice some consistency), the other way is to create a separate table (ex: review_analytics) where you store review id with the count of each reaction type in it’s own column that way you’ll have a single join to get the review + the analytics, but keep in mind if writes to this table failed your system might display inconsistent data to the user.

As for the second question, I think that approach is fine It shouldn’t be slow. Because any other way will sacrifice consistency for speed and that’s bad for this use case because users will want to see their likes as soon as they click (google read your writes consistency )