让 WordPress 只搜索文章的标题

/**
 * 让 WordPress 只搜索文章的标题
 * https://www.wpdaxue.com/search-by-title-only.html
 */
function __search_by_title_only( $search, &$wp_query )
{
	global $wpdb;

	if ( empty( $search ) )
        return $search; // skip processing - no search term in query

    $q = $wp_query->query_vars;    
    $n = ! empty( $q['exact'] ) ? '' : '%';

    $search =
    $searchand = '';

    foreach ( (array) $q['search_terms'] as $term ) {
    	$term = esc_sql( like_escape( $term ) );
    	$search .= "{$searchand}($wpdb->posts.post_title LIKE '{$n}{$term}{$n}')";
    	$searchand = ' AND ';
    }

    if ( ! empty( $search ) ) {
    	$search = " AND ({$search}) ";
    	if ( ! is_user_logged_in() )
    		$search .= " AND ($wpdb->posts.post_password = '') ";
    }

    return $search;
}
add_filter( 'posts_search', '__search_by_title_only', 500, 2 );