Update post fields (counter part to get_post_field()

update_post_fields.php

<?php
/**
 * Update one or more post fields
 *
 * @global wpdb $wpdb
 *
 * @param array       $field Array of field/value pairs to update.
 * @param WP_Post|int $post Post object or id.
 *
 * @return int|bool  Number of updated rows, false on failure.
 */
function update_post_fields( $fields, $post ) {
	global $wpdb;

	if ( ! is_array( $fields ) || empty( $fields ) )
		return;

	if ( ! is_a( $post, 'WP_Post' ) )
		$post = get_post( $post );

	$rows = $wpdb->update( $wpdb->posts, $fields, array( 'ID' => $post->ID ) );

	return $rows;
}