一般情况下， Oracle 子表的外键需要添加索引， 如果外键不添加索引， 一下3种情况会导致 修改父表会锁住子表 1、更新父表主键，
一般情况下， Oracle 子表的外键需要添加索引，
如果外键不添加索引， 一下3种情况会导致 修改父表会锁住子表
1、更新父表主键，子表会被锁住
2、删除父表一行， 整个子表会被锁住
3、合并到父表，子表会被锁住。（9i，，10G是这样，11G不会）。
如果满足以下三种情况，则不需要在外键建立索引
1、没有从父表删除数据
2、没有更新父表主键
3、没有父表关联到子表
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