rm -rf 86725
bin/mysqld --initialize-insecure --basedir=$PWD --datadir=$PWD/86725 -v
bin/mysqld  --basedir=$PWD --datadir=$PWD/86725 --core-file --socket=/tmp/mysql.sock --port=3306 --log-error=$PWD/86725/log.err 2>&1 &

-- 5.7.18
[1] 30648
[umshastr@hod03]/export/umesh/server/binaries/GABuilds/mysql-advanced-5.7.18: bin/mysql -uroot -S /tmp/mysql.sock
Welcome to the MySQL monitor.  Commands end with ; or \g.
Your MySQL connection id is 3
Server version: 5.7.18-enterprise-commercial-advanced MySQL Enterprise Server - Advanced Edition (Commercial)

Copyright (c) 2000, 2017, Oracle and/or its affiliates. All rights reserved.

Oracle is a registered trademark of Oracle Corporation and/or its
affiliates. Other names may be trademarks of their respective
owners.

Type 'help;' or '\h' for help. Type '\c' to clear the current input statement.

root@localhost [(none)]> set sql_mode='';
Query OK, 0 rows affected, 1 warning (0.00 sec)

root@localhost [(none)]> create database test;
Query OK, 1 row affected (0.00 sec)

root@localhost [(none)]> use test
Database changed
root@localhost [test]> CREATE TABLE `test` (
    ->   `col_ttext` TINYTEXT
    -> ) ENGINE=MyISAM DEFAULT CHARSET=ujis;
Query OK, 0 rows affected (0.01 sec)

root@localhost [test]> ALTER TABLE `test` ADD KEY `col_ttext` (`col_ttext`(255));
Query OK, 0 rows affected, 1 warning (0.01 sec)
Records: 0  Duplicates: 0  Warnings: 1

root@localhost [test]> show warnings;
+---------+------+---------------------------------------------------------+
| Level   | Code | Message                                                 |
+---------+------+---------------------------------------------------------+
| Warning | 1071 | Specified key was too long; max key length is 255 bytes |
+---------+------+---------------------------------------------------------+
1 row in set (0.00 sec)

root@localhost [test]> SHOW INDEX FROM `test`;
+-------+------------+-----------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+---------------+
| Table | Non_unique | Key_name  | Seq_in_index | Column_name | Collation | Cardinality | Sub_part | Packed | Null | Index_type | Comment | Index_comment |
+-------+------------+-----------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+---------------+
| test  |          1 | col_ttext |            1 | col_ttext   | A         |        NULL |       85 | NULL   | YES  | BTREE      |         |               |
+-------+------------+-----------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+---------------+
1 row in set (0.00 sec)

root@localhost [test]> ALTER TABLE `test` DROP KEY `col_ttext`;
Query OK, 0 rows affected (0.00 sec)
Records: 0  Duplicates: 0  Warnings: 0

root@localhost [test]> ALTER TABLE `test` ADD UNIQUE KEY `col_ttext` (`col_ttext`(255));
ERROR 1071 (42000): Specified key was too long; max key length is 255 bytes
root@localhost [test]>
root@localhost [test]>

-- 5.7.16

rm -rf 86725
bin/mysqld --initialize-insecure --basedir=$PWD --datadir=$PWD/86725 -v
bin/mysqld  --basedir=$PWD --datadir=$PWD/86725 --core-file --socket=/tmp/mysql.sock --port=3306 --log-error=$PWD/86725/log.err 2>&1 &


[umshastr@hod03]/export/umesh/server/binaries/GABuilds/mysql-advanced-5.7.16-linux-glibc2.5-x86_64: bin/mysql -uroot -S /tmp/mysql.sock
Welcome to the MySQL monitor.  Commands end with ; or \g.
Your MySQL connection id is 2
Server version: 5.7.16-enterprise-commercial-advanced MySQL Enterprise Server - Advanced Edition (Commercial)

Copyright (c) 2000, 2016, Oracle and/or its affiliates. All rights reserved.

Oracle is a registered trademark of Oracle Corporation and/or its
affiliates. Other names may be trademarks of their respective
owners.

Type 'help;' or '\h' for help. Type '\c' to clear the current input statement.

root@localhost [(none)]> set sql_mode='';
Query OK, 0 rows affected, 1 warning (0.00 sec)

root@localhost [(none)]> create database test;
Query OK, 1 row affected (0.00 sec)

root@localhost [(none)]> use test
Database changed
root@localhost [test]> CREATE TABLE `test` (`col_ttext` TINYTEXT) ENGINE=MyISAM DEFAULT CHARSET=ujis;
Query OK, 0 rows affected (0.00 sec)

root@localhost [test]> ALTER TABLE `test` ADD KEY `col_ttext` (`col_ttext`(255));
Query OK, 0 rows affected (0.01 sec)
Records: 0  Duplicates: 0  Warnings: 0

root@localhost [test]> SHOW INDEX FROM `test`;
+-------+------------+-----------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+---------------+
| Table | Non_unique | Key_name  | Seq_in_index | Column_name | Collation | Cardinality | Sub_part | Packed | Null | Index_type | Comment | Index_comment |
+-------+------------+-----------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+---------------+
| test  |          1 | col_ttext |            1 | col_ttext   | A         |        NULL |      255 | NULL   | YES  | BTREE      |         |               |
+-------+------------+-----------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+---------------+
1 row in set (0.00 sec)

root@localhost [test]> ALTER TABLE `test` DROP KEY `col_ttext`;
Query OK, 0 rows affected (0.01 sec)
Records: 0  Duplicates: 0  Warnings: 0

root@localhost [test]> ALTER TABLE `test` ADD UNIQUE KEY `col_ttext` (`col_ttext`(255));
Query OK, 0 rows affected (0.00 sec)
Records: 0  Duplicates: 0  Warnings: 0

root@localhost [test]> SHOW INDEX FROM `test`;
+-------+------------+-----------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+---------------+
| Table | Non_unique | Key_name  | Seq_in_index | Column_name | Collation | Cardinality | Sub_part | Packed | Null | Index_type | Comment | Index_comment |
+-------+------------+-----------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+---------------+
| test  |          0 | col_ttext |            1 | col_ttext   | A         |        NULL |      255 | NULL   | YES  | BTREE      |         |               |
+-------+------------+-----------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+---------------+
1 row in set (0.00 sec)

root@localhost [test]>