Do I understand MySQL optimization correctly?

Question

MySQL

I am new to MySQL.
I have a posts table with many fields (more than 20)
If I make an index table with the id_post fields (which points to the post id in posts) and the url field (by which we will search for the post).
Will such a query be optimized, unlike if I directly access a table where there are many fields?
If there are links to sensible materials - write!

Answer 1

If I understand you, then you think that the number of table fields will affect performance. No, because this is a delusion. It is better to create indexes to you for these two fields. And an additional table with exhaustive data is evil against the form of a normal relational one. Suppose you have already found data on your table, but then you need additional fields, what will happen then?

Answer 2

Read about normal forms