[8.1.基本概念](8.1.%E5%9F%BA%E6%9C%AC%E6%A6%82%E5%BF%B5.md) [8.2.一对一关系](8.2.%E4%B8%80%E5%AF%B9%E4%B8%80%E5%85%B3%E7%B3%BB.md) [8.3.一对多关系](8.3.%E4%B8%80%E5%AF%B9%E5%A4%9A%E5%85%B3%E7%B3%BB.md) [8.4.多对多关系](8.4.%E5%A4%9A%E5%AF%B9%E5%A4%9A%E5%85%B3%E7%B3%BB.md)