create table t1 (f1 tinyblob not null) engine=innodb;
alter table t1 add unique index (f1(255));
drop table t1;
create table t1 (f1 tinyblob not null) engine=innodb;
alter table t1 add unique index (f1(356));
show create table t1;
Table	Create Table
t1	CREATE TABLE `t1` (
  `f1` tinyblob NOT NULL,
  UNIQUE KEY `f1` (`f1`(255))
) ENGINE=InnoDB DEFAULT CHARSET=latin1
drop table t1;
create table t1 (f1 point not null) engine=innodb;
alter table t1 add unique index (f1);
drop table t1;