addSelect() public method
Add more columns to the SELECT part of the query. Note, that if select() has not been specified before, you should include * explicitly if you want to select all remaining columns too: $query->addSelect(["*", "CONCAT(first_name, ' ', last_name) AS full_name"])->one();
See also select().
public $this addSelect ( $columns )$columns
string|array|yii\db\Expression
The columns to add to the select. See select() for more details about the format of this param