\Drupal::database()->select with Expression used as Condition
// Where Expressions
    $query-&gt;where('WEEK(sd.field_start_date_value) = :weekNo', array(':weekNo' =&gt; $weekNo));
    $query-&gt;where('WEEK(sd.field_start_date_value) = :weekYr', array(':weekYr' =&gt; $weekYr));


Apparently this can be achieved with $query->where();