MySQL Query index

Can MySQL use the index in a like query? Where do you use the index?

When using like, if you use ' percent ', will you use the index?
EXPLAIN SELECT * from ' user ' WHERE username like '%ptd_% ';  The result above is a full table scan (type = = All) and is not used to the index.  Just use a% query result: EXPLAIN SELECT * from ' user ' WHERE username like ' ptd_% '; this is used to index (type = = range). EXPLAIN SELECT * from ' user ' where username like '%ptd_ '; in front of use% is also full table scan, not used to index. In summary, MySQL uses a like query only when it does not start with a%, the index is used.

MySQL Query index