ORACLE 数据库设计 多对多关系
关于数据库两张表多对多的关系设计，之前以为多对多关系，只要两张表存在各自对方表的主键就行。殊不知这种理解是错误的，今天借此时间总结一下。 数据库多对多表设计，假设使用主外键关系设计多对多表关系，会造成： 1、对一张表进行DML语句时，该表对应的
关于数据库两张表多对多的关系设计，之前以为多对多关系，只要两张表存在各自对方表的主键就行。殊不知这种理解是错误的，今天借此时间总结一下。
数据库多对多表设计，假设使用主外键关系设计多对多表关系，会造成：
1、对一张表进行DML语句时，该表对应的外键会影响另外一张表的数据，产生级联删除问题；
2、因为是多对多的关系，会产生大量冗余数据；
--假设以上2种都允许存在，系统将就凑合也还可用。致命一点是：
3、多对多关系，会导致主键重复（主键是不可重复的！！！）。
故对于多对多关系表设计，必须使用中间表进行管理，各自表的主键构成中间表的联合主键。
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