数据库主键区别的相关内容

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阿里云文档 2023-09-03

触发器和规则系统规则vs触发器有哪些区别？_云原生数据库PolarDB PostgreSQL版（兼容Oracle）_云原生数据库 PolarDB(PolarDB)

许多触发器可以干的事情同样也可以用PostgreSQL规则系统来实现。目前不能用规则来实现的东西之一是某些约束，特别是外键。可以放置一个合格的规则在一列上，这个规则在列的值没有出现在另一个表中时把命令重写成NOTHING。但是这样做数据就会被不声不响地丢弃，因此也不是一个好主意。如果要求检查值的有效性，并且在出现无效值的情况下应该生成一个错误消息，这种需求就必须要用触发器来完成。

文章 2022-06-13 来自：开发者社区

数据库中的主键、外键、索引的区别

定义：主键--唯一标识一条记录，不能有重复的，不允许为空外键--表的外键是另一表的主键, 外键可以有重复的, 可以是空值索引--该字段没有重复值，但可以有一个空值作用：主键--用来保证数据完整性外键--用来和其他表建立联系用的索引--是提高查询排序的速度个数：主键--主键只能有一个外键--一个表可以有多个外键索引--一个表可以有多个唯一索引

文章 2022-02-14 来自：开发者社区

数据库面试题【十九、count(字段) &count(主键 id) &count(1)&count(*)的区别】

count(可空字段)扫描全表，读到server层，判断字段可空，拿出该字段所有值，判断每一个值是否为空，不为空则累加count(非空字段)与count(主键 id)扫描全表，读到server层，判断字段不可空，按行累加。count(1)扫描全表，但不取值，server层收到的每一行都是1，判断不可能是null，按值累加。注意：count(1)执行速度比count(主键 id)快的原因：从引擎返....

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数据库审计

满足等保2.0二级和三级 “安全审计”合规要求的同时，智能解析数据库通信流量，细粒度审计数据库访问行为，通过对数据库全量行为的审计溯源、危险攻击的实时告警、风险语句的智能预警，提供数据库资产最安全的监控保障。

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