mysql optimization - Will the mysql like statement cause a full table scan?

Question

select id from t where name like '%abc%'

Answer 1

Fuzzy query, even if you have an index, you don’t know whether there are these three letters in the index or whether they are arranged in this position or in this row. . .

Answer 2

Not necessarily depends on the query conditions.
If it matches the left prefix, you can use the index
For example like abc%

Answer 3

Same as above, try not to blur like in sql. If the amount of data is large, it will be messed up.