WordPress at a glance
function is not described

wp_upgrade() WP 2.1.0

Runs WordPress Upgrade functions.

Upgrades the database if needed during a site update.

  • Global. Int. $wp_current_db_version
  • Global. Int. $wp_db_version
  • Global. wpdb. $wpdb WordPress database abstraction object.
Hooks in function
Return

Nothing (null).

Usage

wp_upgrade();

Code of wp upgrade: wp-admin/includes/upgrade.php WP 5.2.2

<?php
function wp_upgrade() {
	global $wp_current_db_version, $wp_db_version, $wpdb;

	$wp_current_db_version = __get_option( 'db_version' );

	// We are up-to-date. Nothing to do.
	if ( $wp_db_version == $wp_current_db_version ) {
		return;
	}

	if ( ! is_blog_installed() ) {
		return;
	}

	wp_check_mysql_version();
	wp_cache_flush();
	pre_schema_upgrade();
	make_db_current_silent();
	upgrade_all();
	if ( is_multisite() && is_main_site() ) {
		upgrade_network();
	}
	wp_cache_flush();

	if ( is_multisite() ) {
		$site_id = get_current_blog_id();

		if ( $wpdb->get_row( $wpdb->prepare( "SELECT blog_id FROM {$wpdb->blog_versions} WHERE blog_id = %d", $site_id ) ) ) {
			$wpdb->query( $wpdb->prepare( "UPDATE {$wpdb->blog_versions} SET db_version = %d WHERE blog_id = %d", $wp_db_version, $site_id ) );
		} else {
			$wpdb->query( $wpdb->prepare( "INSERT INTO {$wpdb->blog_versions} ( `blog_id` , `db_version` , `last_updated` ) VALUES ( %d, %d, NOW() );", $site_id, $wp_db_version ) );
		}
	}

	/**
	 * Fires after a site is fully upgraded.
	 *
	 * @since 3.9.0
	 *
	 * @param int $wp_db_version         The new $wp_db_version.
	 * @param int $wp_current_db_version The old (current) $wp_db_version.
	 */
	do_action( 'wp_upgrade', $wp_db_version, $wp_current_db_version );
}