protected function getAlterTableChangeColumnClause(ColumnDiff $columnDiff)
    {
        $column = $columnDiff->column;

        // Do not return alter clause if only comment has changed.
        if (! ($columnDiff->hasChanged('comment') && count($columnDiff->changedProperties) === 1)) {
            $columnAlterationClause = 'ALTER ' .
                $this->getColumnDeclarationSQL($column->getQuotedName($this), $column->toArray());

            if ($columnDiff->hasChanged('default') && $column->getDefault() === null) {
                $columnAlterationClause .= ', ALTER ' . $column->getQuotedName($this) . ' DROP DEFAULT';
            }

            return $columnAlterationClause;
        }

        return null;
    }