Why this query is fast

Welcome to another database question. In this question I created a community poll question and provided some answers. All answers can be correct of course but the question is what is the most efficient? this is what I try to explore in this video and compare how different database platforms such as mysql or Postgres differ in those implementations;

Table T with three integer fields A, B and C.

A has a primary key clustered index.

B has a secondary index.

Which query is more likely to be the most efficient?

0:00 Intro

1:00 The Question

3:20 WHERE C BETWEEN 50,50000

5:30 WHERE B BETWEEN 50,50000

13:20 WHERE C BETWEEN 50,50000

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