create table bug51378 ( col1 int not null, col2 blob not null, col3 time not null) engine = innodb; create unique index idx on bug51378(col1, col2(31)); alter table bug51378 add unique index idx2(col1, col2(31)); Warnings: Note 1831 Duplicate index `idx2`. This is deprecated and will be disallowed in a future release create unique index idx3 on bug51378(col1, col3); SHOW CREATE TABLE bug51378; Table Create Table bug51378 CREATE TABLE `bug51378` ( `col1` int(11) NOT NULL, `col2` blob NOT NULL, `col3` time NOT NULL, UNIQUE KEY `idx3` (`col1`,`col3`), UNIQUE KEY `idx` (`col1`,`col2`(31)), UNIQUE KEY `idx2` (`col1`,`col2`(31)) ) ENGINE=InnoDB DEFAULT CHARSET=latin1 COLLATE=latin1_swedish_ci drop index idx3 on bug51378; SHOW CREATE TABLE bug51378; Table Create Table bug51378 CREATE TABLE `bug51378` ( `col1` int(11) NOT NULL, `col2` blob NOT NULL, `col3` time NOT NULL, UNIQUE KEY `idx` (`col1`,`col2`(31)), UNIQUE KEY `idx2` (`col1`,`col2`(31)) ) ENGINE=InnoDB DEFAULT CHARSET=latin1 COLLATE=latin1_swedish_ci alter table bug51378 add primary key idx3(col1, col2(31)); Warnings: Warning 1280 Name 'idx3' ignored for PRIMARY key. SHOW CREATE TABLE bug51378; Table Create Table bug51378 CREATE TABLE `bug51378` ( `col1` int(11) NOT NULL, `col2` blob NOT NULL, `col3` time NOT NULL, PRIMARY KEY (`col1`,`col2`(31)), UNIQUE KEY `idx` (`col1`,`col2`(31)), UNIQUE KEY `idx2` (`col1`,`col2`(31)) ) ENGINE=InnoDB DEFAULT CHARSET=latin1 COLLATE=latin1_swedish_ci drop table bug51378; create table bug51378 ( col1 int not null, col2 blob not null, col3 time not null, primary key(col1, col2(31))) engine = innodb; create unique index idx on bug51378(col1, col2(31)); SHOW CREATE TABLE bug51378; Table Create Table bug51378 CREATE TABLE `bug51378` ( `col1` int(11) NOT NULL, `col2` blob NOT NULL, `col3` time NOT NULL, PRIMARY KEY (`col1`,`col2`(31)), UNIQUE KEY `idx` (`col1`,`col2`(31)) ) ENGINE=InnoDB DEFAULT CHARSET=latin1 COLLATE=latin1_swedish_ci drop table bug51378; create table bug51378 ( col1 int not null, col2 int ) engine = innodb; create unique index idx on bug51378(col1, col2); SHOW CREATE TABLE bug51378; Table Create Table bug51378 CREATE TABLE `bug51378` ( `col1` int(11) NOT NULL, `col2` int(11) DEFAULT NULL, UNIQUE KEY `idx` (`col1`,`col2`) ) ENGINE=InnoDB DEFAULT CHARSET=latin1 COLLATE=latin1_swedish_ci drop table bug51378;