Can there be function-based indexes in MySQL?

In below5.6In MySQL versions below, you cannot use function-based indexes. First, to create a function-based index in MySQL, we will create a table.

mysql> create table FunctionIndexDemo
　　　-　> (
　　　-　> FirstName varchar(100)
　　　-　> );

Let's see the syntax for creating an index based on a function.

create index index_name on yourTableName (columnName(IntegerSize));

This is the query.

mysql> create index indFirstName on FunctionIndexDemo (FirstName(6));
Records: 0 Duplicates: 0 Warnings: 0

Check if the index exists.

mysql> SHOW INDEX FROM FunctionIndexDemo;

This is the output.

+-------------------+------------+--------------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+---------------+---------+
| Table | Non_unique | Key_name | Seq_in_index | Column_name | Collation | Cardinality | Sub_part | Packed | Null | Index_type | Comment | Index_comment | Visible |
+-------------------+------------+--------------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+---------------+---------+
| functionindexdemo |　　　　　　　　　　1　| indFirstName |　　　　　　　　　　　　1　| FirstName | A | | 0 |　　　　　　　　6　| NULL | YES | BTREE | | | YES |
+-------------------+------------+--------------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+---------------+---------+
1　row in set (0.24　sec)