set @@sql_mode=strict_trans_tables;
create table t1(a text not null) row_format=dynamic engine=innodb;
create index idx1 on t1(a(3073));
Warnings:
Note	1071	Specified key was too long; max key length is 3072 bytes
show create table t1;
Table	Create Table
t1	CREATE TABLE `t1` (
  `a` text NOT NULL,
  KEY `idx1` (`a`(3072))
) ENGINE=InnoDB DEFAULT CHARSET=latin1 ROW_FORMAT=DYNAMIC
drop table t1;
set @@sql_mode=default;
create table t1 (
id1    int(11)      not null auto_increment,
id2    varchar(30)  not null,
id3    datetime     not null default current_timestamp,
primary key (id1),
unique key unique_id2 (id2)
) engine=innodb;
alter table t1 change column id2 id4 varchar(100) not null;
select * from t1 where id4 like 'a';
id1	id4	id3
drop table t1;