Date.php

<?php

namespace Drupal\views\Plugin\views\sort;

use Drupal\Core\Form\FormStateInterface;

/**
 * Basic sort handler for dates.
 *
 * This handler enables granularity, which is the ability to make dates
 * equivalent based upon nearness.
 *
 * @ViewsSort("date")
 */
class Date extends SortPluginBase {
    protected function defineOptions() {
        $options = parent::defineOptions();
        $options['granularity'] = [
            'default' => 'second',
        ];
        return $options;
    }
    public function buildOptionsForm(&$form, FormStateInterface $form_state) {
        parent::buildOptionsForm($form, $form_state);
        $form['granularity'] = [
            '#type' => 'radios',
            '#title' => $this->t('Granularity'),
            '#options' => [
                'second' => $this->t('Second'),
                'minute' => $this->t('Minute'),
                'hour' => $this->t('Hour'),
                'day' => $this->t('Day'),
                'month' => $this->t('Month'),
                'year' => $this->t('Year'),
            ],
            '#description' => $this->t('The granularity is the smallest unit to use when determining whether two dates are the same; for example, if the granularity is "Year" then all dates in 1999, regardless of when they fall in 1999, will be considered the same date.'),
            '#default_value' => $this->options['granularity'],
        ];
    }
    
    /**
     * Called to add the sort to a query.
     */
    public function query() {
        $this->ensureMyTable();
        switch ($this->options['granularity']) {
            case 'second':
            default:
                $this->query
                    ->addOrderBy($this->tableAlias, $this->realField, $this->options['order']);
                return;
            case 'minute':
                $formula = $this->getDateFormat('YmdHi');
                break;
            case 'hour':
                $formula = $this->getDateFormat('YmdH');
                break;
            case 'day':
                $formula = $this->getDateFormat('Ymd');
                break;
            case 'month':
                $formula = $this->getDateFormat('Ym');
                break;
            case 'year':
                $formula = $this->getDateFormat('Y');
                break;
        }
        // Add the field.
        $this->query
            ->addOrderBy(NULL, $formula, $this->options['order'], $this->tableAlias . '_' . $this->field . '_' . $this->options['granularity']);
    }

}