If you’re interviewing for a backend position dealing with lots of data, your interview might ask you this question.

Source: I’ve been asked this question before in the distant past

My (wrong) past answer + train of thought

In SQL, we do lots of SELECT * FROM table_name WHERE id = SOME_ID

The fastest way to access one value would be to use a dictionary (hashmap)

Me: A SQL table probably uses a dictionary data structure as it takes O(1) time to access a certain entry by id.

My interviewer then made a face

He wasn’t too impressed.

Interviewer: But what if I want to find many entries from indexes say 50–100? Would a dictionary still be the best choice?

Me: (oops dictionary isn’t the right answer)

Me: Hm maybe it’s a list (proceeds to spout some gibberish)

B-tree.

Let’s say our table stores 400 dog entries.

There are 2 types of nodes: