Configuring UNIQUE constraint in MYSQL to avoid duplicate entries for a given column/field

MySQL Query:

ALTER TABLE `MyLabDB`.`testusers` DROP INDEX `username` ,
ADD UNIQUE `username` ( `username` ) COMMENT ‘Avoid duplicate entries for username’;

phpMyAdmin GUI:

After setting the Unique Index for the field, whenever a duplicate entry is attempted for insertion, mySQL will result in “#1062” error as shown below:

#1062 – Duplicate entry ‘user9’ for key ‘username’

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