Are the columns "separately" indexed, or do they need to be specified explicitly?

Question

MySQL

I add a unique index on two columns. If there is a select/sort/etc on one of them, do I need to add a separate index for one column? In other words, are the columns indexed "separately", or does it have to be explicitly specified?
ALTER TABLE `table` ADD UNIQUE (`col1`, `col2`)

Answer 1

Columns are not individually indexed, but conditional queries with the first of the specified columns can use a composite index.
Few examples:
Will use index
Will also use the index
The index will not be used.
And in this query, although the index will be used, but only for col1. For col2 - full view of the table.
The index will be used for WHERE, but not for ORDER BY.