Database\Storage eventually needs a way to represent database functions and expressions.

Functions sitting in a namespace could be very useful for this, because then you can use concise function names that read well.

use function Darya\Database\Storage\Query\Function\concat;

$results = $storage->query('users')
    ->where(concat('firstname', 'surname'), '=', 'Alexa')
    ->run();

Under the hood these helpers would just instantiate the relevant objects for the query to hold, which the translators will then use to generate SQL.