src/SelectQuery.php
public function groupBy(string ...$field)
    {
        $this->changed = true;
        $this->groupBy = $field;

        return $this;
    }
public function groupBy(string ...$field)
    {
        $this->changed = true;
        $this->groupBy = $field;

        return $this;
    }
Set grouping fields to the query.

@param string $field
@return self