"A real friend is one who walks in when the rest of the world walks out".这是什么句型

A real friend is one (who walks in when the rest of the world walks out)
主语 系动词 表语 定语从句
who walks in （ when the rest of the world walks out）
从句主语 从句谓语 副词作状语 时间状语从句
when （the rest of the world） walks out
从句主语 从句谓语 副词作状语