Is a UNIQUE INDEX lookup faster than a non-UNIQUE lookup?

Question

SQL

One experienced person here told me that there is no difference. The understanding of the world is shaken.

I started looking and reading about it wherever possible. I found several articles explaining that there is a performance gain when searching for unique ones . But then I remembered that by index, the search usually takes place in a binary tree, and it has several values ​​\u200b\u200bthat lie in one node, which means the speed should not differ. So what is true and what is not?

I will not conduct tests, it is not possible to create conditions for adequate testing

Answer 1

The central indicator of the effectiveness of the index is selectivity. For unique values, it is maximum.

Answer 2

UNIQUE is primarily about restrictions, it is strange to compare them in this way, if you do not have such a condition, then you will not be able to apply UNIQUE, and if there is, then why it was not immediately applied (well, except for rare reasons)

Answer 3

If the index data is unique, then theoretically they are the same. In practice, this depends on optimizations in the DBMS.
UNIQUE INDEX guarantees that the data will be unique, while a simple index is not.