// a1 needs to be unique ['a1', 'unique'] // a1 needs to be unique, but column a2 will be used to check the uniqueness of the a1 value ['a1', 'unique', 'targetAttribute' => 'a2'] // a1 and a2 need to be unique together, and they both will receive error message [['a1', 'a2'], 'unique', 'targetAttribute' => ['a1', 'a2']] // a1 and a2 need to be unique together, only a1 will receive error message ['a1', 'unique', 'targetAttribute' => ['a1', 'a2']] // a1 needs to be unique by checking the uniqueness of both a2 and a3 (using a1 value) ['a1', 'unique', 'targetAttribute' => ['a2', 'a1' => 'a3']]
https://www.yiiframework.com/doc/api/2.0/yii-validators-uniquevalidator