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function is not described

_find_post_by_old_date() WP 4.9.3

Find the post ID for redirecting an old date.

This is an internal function for using it by WP core itself. It's not recommended to use this function in your code.

No Hooks.

Return

Int. The Post ID.

Usage

_find_post_by_old_date( $post_type );
$post_type(string) (required)
The current post type based on the query vars.

Notes

Changelog

Since 4.9.3 Introduced.

Code of _find_post_by_old_date() WP 5.8

<?php
function _find_post_by_old_date( $post_type ) {
	global $wpdb;

	$date_query = '';
	if ( get_query_var( 'year' ) ) {
		$date_query .= $wpdb->prepare( ' AND YEAR(pm_date.meta_value) = %d', get_query_var( 'year' ) );
	}
	if ( get_query_var( 'monthnum' ) ) {
		$date_query .= $wpdb->prepare( ' AND MONTH(pm_date.meta_value) = %d', get_query_var( 'monthnum' ) );
	}
	if ( get_query_var( 'day' ) ) {
		$date_query .= $wpdb->prepare( ' AND DAYOFMONTH(pm_date.meta_value) = %d', get_query_var( 'day' ) );
	}

	$id = 0;
	if ( $date_query ) {
		$id = (int) $wpdb->get_var( $wpdb->prepare( "SELECT post_id FROM $wpdb->postmeta AS pm_date, $wpdb->posts WHERE ID = post_id AND post_type = %s AND meta_key = '_wp_old_date' AND post_name = %s" . $date_query, $post_type, get_query_var( 'name' ) ) );

		if ( ! $id ) {
			// Check to see if an old slug matches the old date.
			$id = (int) $wpdb->get_var( $wpdb->prepare( "SELECT ID FROM $wpdb->posts, $wpdb->postmeta AS pm_slug, $wpdb->postmeta AS pm_date WHERE ID = pm_slug.post_id AND ID = pm_date.post_id AND post_type = %s AND pm_slug.meta_key = '_wp_old_slug' AND pm_slug.meta_value = %s AND pm_date.meta_key = '_wp_old_date'" . $date_query, $post_type, get_query_var( 'name' ) ) );
		}
	}

	return $id;
}