MySQL base, utf8mb4 encoding. What encoding to put for a string identifier?

Question

MySQL

The VARCHAR field is 255 long, which is too long for a utf8mb4-encoded index
Characters: a-z0-9_- Case insensitive
.
ascii_general_ci?
And is it true that the field only with Latin does not care at all with what encoding we connect to the database?

Answer 1

Even more suitable is ascii_bin - which is case sensitive (identifier is the same)