MySQL 5.7

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CREATE TABLE `test` (
  `user_id` int(11) NOT NULL,
  `comment` varchar(45) NOT NULL,
  PRIMARY KEY (`user_id`)
) ENGINE=InnoDB DEFAULT CHARSET=latin1 COMMENT='no';
ALTER TABLE test DROP PRIMARY KEY 
ALTER TABLE test ADD INDEX (user_id)
REPLACE INTO test (
user_id,
comment
)
VALUES
(111, 'ANDROID'),
(111, 'IOS')
SELECT *
FROM test


user_id
comment


111
ANDROID

111
IOS


ALTER TABLE test ADD UNIQUE (comment)
REPLACE INTO test (
user_id,
comment
)
VALUES
(111, 'ANDROID'),
(111, 'COMMODORE')
SELECT *
FROM test


user_id
comment


111
ANDROID

111
COMMODORE

111
IOS