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## 21个写SQL的好习惯

![](http://img.topjavaer.cn/img/202308030823049.png)

![2](http://img.topjavaer.cn/img/202308030823148.png)

![3](http://img.topjavaer.cn/img/202308030823229.png)

![4](http://img.topjavaer.cn/img/202308030823834.png)

![5](http://img.topjavaer.cn/img/202308030824651.png)

![6](http://img.topjavaer.cn/img/202308030824461.png)

![7](http://img.topjavaer.cn/img/202308030824900.png)

![8](http://img.topjavaer.cn/img/202308030824354.png)

![9](http://img.topjavaer.cn/img/202308030824755.png)





## MySQL面试题

下面分享MySQL常考的**面试题目**。

- [事务的四大特性？](https://topjavaer.cn/database/mysql.html#%E4%BA%8B%E5%8A%A1%E7%9A%84%E5%9B%9B%E5%A4%A7%E7%89%B9%E6%80%A7)
- [数据库的三大范式](https://topjavaer.cn/database/mysql.html#%E6%95%B0%E6%8D%AE%E5%BA%93%E7%9A%84%E4%B8%89%E5%A4%A7%E8%8C%83%E5%BC%8F)
- [事务隔离级别有哪些？](https://topjavaer.cn/database/mysql.html#%E4%BA%8B%E5%8A%A1%E9%9A%94%E7%A6%BB%E7%BA%A7%E5%88%AB%E6%9C%89%E5%93%AA%E4%BA%9B)
- [生产环境数据库一般用的什么隔离级别呢？](https://topjavaer.cn/database/mysql.html#%E7%94%9F%E4%BA%A7%E7%8E%AF%E5%A2%83%E6%95%B0%E6%8D%AE%E5%BA%93%E4%B8%80%E8%88%AC%E7%94%A8%E7%9A%84%E4%BB%80%E4%B9%88%E9%9A%94%E7%A6%BB%E7%BA%A7%E5%88%AB%E5%91%A2)
- [编码和字符集的关系](https://topjavaer.cn/database/mysql.html#%E7%BC%96%E7%A0%81%E5%92%8C%E5%AD%97%E7%AC%A6%E9%9B%86%E7%9A%84%E5%85%B3%E7%B3%BB)
- [utf8和utf8mb4的区别](https://topjavaer.cn/database/mysql.html#utf8%E5%92%8Cutf8mb4%E7%9A%84%E5%8C%BA%E5%88%AB)
- [什么是索引？](https://topjavaer.cn/database/mysql.html#%E4%BB%80%E4%B9%88%E6%98%AF%E7%B4%A2%E5%BC%95)
- [索引的优缺点？](https://topjavaer.cn/database/mysql.html#%E7%B4%A2%E5%BC%95%E7%9A%84%E4%BC%98%E7%BC%BA%E7%82%B9)
- [索引的作用？](https://topjavaer.cn/database/mysql.html#%E7%B4%A2%E5%BC%95%E7%9A%84%E4%BD%9C%E7%94%A8)
- [什么情况下需要建索引？](https://topjavaer.cn/database/mysql.html#%E4%BB%80%E4%B9%88%E6%83%85%E5%86%B5%E4%B8%8B%E9%9C%80%E8%A6%81%E5%BB%BA%E7%B4%A2%E5%BC%95)
- [什么情况下不建索引？](https://topjavaer.cn/database/mysql.html#%E4%BB%80%E4%B9%88%E6%83%85%E5%86%B5%E4%B8%8B%E4%B8%8D%E5%BB%BA%E7%B4%A2%E5%BC%95)
- [索引的数据结构](https://topjavaer.cn/database/mysql.html#%E7%B4%A2%E5%BC%95%E7%9A%84%E6%95%B0%E6%8D%AE%E7%BB%93%E6%9E%84)
- [Hash索引和B+树索引的区别？](https://topjavaer.cn/database/mysql.html#hash%E7%B4%A2%E5%BC%95%E5%92%8Cb%E6%A0%91%E7%B4%A2%E5%BC%95%E7%9A%84%E5%8C%BA%E5%88%AB)
- [为什么B+树比B树更适合实现数据库索引？](https://topjavaer.cn/database/mysql.html#%E4%B8%BA%E4%BB%80%E4%B9%88b%E6%A0%91%E6%AF%94b%E6%A0%91%E6%9B%B4%E9%80%82%E5%90%88%E5%AE%9E%E7%8E%B0%E6%95%B0%E6%8D%AE%E5%BA%93%E7%B4%A2%E5%BC%95)
- [索引有什么分类？](https://topjavaer.cn/database/mysql.html#%E7%B4%A2%E5%BC%95%E6%9C%89%E4%BB%80%E4%B9%88%E5%88%86%E7%B1%BB)
- [什么是最左匹配原则？](https://topjavaer.cn/database/mysql.html#%E4%BB%80%E4%B9%88%E6%98%AF%E6%9C%80%E5%B7%A6%E5%8C%B9%E9%85%8D%E5%8E%9F%E5%88%99)
- [什么是聚集索引？](https://topjavaer.cn/database/mysql.html#%E4%BB%80%E4%B9%88%E6%98%AF%E8%81%9A%E9%9B%86%E7%B4%A2%E5%BC%95)
- [什么是覆盖索引？](https://topjavaer.cn/database/mysql.html#%E4%BB%80%E4%B9%88%E6%98%AF%E8%A6%86%E7%9B%96%E7%B4%A2%E5%BC%95)
- [索引的设计原则？](https://topjavaer.cn/database/mysql.html#%E7%B4%A2%E5%BC%95%E7%9A%84%E8%AE%BE%E8%AE%A1%E5%8E%9F%E5%88%99)
- [索引什么时候会失效？](https://topjavaer.cn/database/mysql.html#%E7%B4%A2%E5%BC%95%E4%BB%80%E4%B9%88%E6%97%B6%E5%80%99%E4%BC%9A%E5%A4%B1%E6%95%88)
- [什么是前缀索引？](https://topjavaer.cn/database/mysql.html#%E4%BB%80%E4%B9%88%E6%98%AF%E5%89%8D%E7%BC%80%E7%B4%A2%E5%BC%95)
- [索引下推](https://topjavaer.cn/database/mysql.html#%E7%B4%A2%E5%BC%95%E4%B8%8B%E6%8E%A8)
- [常见的存储引擎有哪些？](https://topjavaer.cn/database/mysql.html#%E5%B8%B8%E8%A7%81%E7%9A%84%E5%AD%98%E5%82%A8%E5%BC%95%E6%93%8E%E6%9C%89%E5%93%AA%E4%BA%9B)
- [MyISAM和InnoDB的区别？](https://topjavaer.cn/database/mysql.html#myisam%E5%92%8Cinnodb%E7%9A%84%E5%8C%BA%E5%88%AB)
- [MySQL有哪些锁？](https://topjavaer.cn/database/mysql.html#mysql%E6%9C%89%E5%93%AA%E4%BA%9B%E9%94%81)
- [MVCC 实现原理？](https://topjavaer.cn/database/mysql.html#mvcc-%E5%AE%9E%E7%8E%B0%E5%8E%9F%E7%90%86)
- [快照读和当前读](https://topjavaer.cn/database/mysql.html#%E5%BF%AB%E7%85%A7%E8%AF%BB%E5%92%8C%E5%BD%93%E5%89%8D%E8%AF%BB)
- [共享锁和排他锁](https://topjavaer.cn/database/mysql.html#%E5%85%B1%E4%BA%AB%E9%94%81%E5%92%8C%E6%8E%92%E4%BB%96%E9%94%81)
- [bin log/redo log/undo log](https://topjavaer.cn/database/mysql.html#bin-logredo-logundo-log)
- [bin log和redo log有什么区别？](https://topjavaer.cn/database/mysql.html#bin-log%E5%92%8Credo-log%E6%9C%89%E4%BB%80%E4%B9%88%E5%8C%BA%E5%88%AB)
- [讲一下MySQL架构？](https://topjavaer.cn/database/mysql.html#%E8%AE%B2%E4%B8%80%E4%B8%8Bmysql%E6%9E%B6%E6%9E%84)
- [分库分表](https://topjavaer.cn/database/mysql.html#%E5%88%86%E5%BA%93%E5%88%86%E8%A1%A8)
- [什么是分区表？](https://topjavaer.cn/database/mysql.html#%E4%BB%80%E4%B9%88%E6%98%AF%E5%88%86%E5%8C%BA%E8%A1%A8)
- [分区表类型](https://topjavaer.cn/database/mysql.html#%E5%88%86%E5%8C%BA%E8%A1%A8%E7%B1%BB%E5%9E%8B)
- [分区的问题？](https://topjavaer.cn/database/mysql.html#%E5%88%86%E5%8C%BA%E7%9A%84%E9%97%AE%E9%A2%98)
- [查询语句执行流程？](https://topjavaer.cn/database/mysql.html#%E6%9F%A5%E8%AF%A2%E8%AF%AD%E5%8F%A5%E6%89%A7%E8%A1%8C%E6%B5%81%E7%A8%8B)
- [更新语句执行过程？](https://topjavaer.cn/database/mysql.html#%E6%9B%B4%E6%96%B0%E8%AF%AD%E5%8F%A5%E6%89%A7%E8%A1%8C%E8%BF%87%E7%A8%8B)
- [exist和in的区别？](https://topjavaer.cn/database/mysql.html#exist%E5%92%8Cin%E7%9A%84%E5%8C%BA%E5%88%AB)
- [MySQL中int()和char()的区别？](https://topjavaer.cn/database/mysql.html#mysql%E4%B8%ADint10%E5%92%8Cchar10%E7%9A%84%E5%8C%BA%E5%88%AB)
- [truncate、delete与drop区别？](https://topjavaer.cn/database/mysql.html#truncatedelete%E4%B8%8Edrop%E5%8C%BA%E5%88%AB)
- [having和where区别？](https://topjavaer.cn/database/mysql.html#having%E5%92%8Cwhere%E5%8C%BA%E5%88%AB)
- [什么是MySQL主从同步？](https://topjavaer.cn/database/mysql.html#%E4%BB%80%E4%B9%88%E6%98%AFmysql%E4%B8%BB%E4%BB%8E%E5%90%8C%E6%AD%A5)
- [为什么要做主从同步？](https://topjavaer.cn/database/mysql.html#%E4%B8%BA%E4%BB%80%E4%B9%88%E8%A6%81%E5%81%9A%E4%B8%BB%E4%BB%8E%E5%90%8C%E6%AD%A5)
- [乐观锁和悲观锁是什么？](https://topjavaer.cn/database/mysql.html#%E4%B9%90%E8%A7%82%E9%94%81%E5%92%8C%E6%82%B2%E8%A7%82%E9%94%81%E6%98%AF%E4%BB%80%E4%B9%88)
- [用过processlist吗？](https://topjavaer.cn/database/mysql.html#%E7%94%A8%E8%BF%87processlist%E5%90%97)
- [MySQL查询 limit 1000,10 和limit 10 速度一样快吗？](https://topjavaer.cn/database/mysql.html#mysql%E6%9F%A5%E8%AF%A2-limit-100010-%E5%92%8Climit-10-%E9%80%9F%E5%BA%A6%E4%B8%80%E6%A0%B7%E5%BF%AB%E5%90%97)
- [深分页怎么优化？](https://topjavaer.cn/database/mysql.html#%E6%B7%B1%E5%88%86%E9%A1%B5%E6%80%8E%E4%B9%88%E4%BC%98%E5%8C%96)
- [高度为3的B+树，可以存放多少数据？](https://topjavaer.cn/database/mysql.html#%E9%AB%98%E5%BA%A6%E4%B8%BA3%E7%9A%84b%E6%A0%91%E5%8F%AF%E4%BB%A5%E5%AD%98%E6%94%BE%E5%A4%9A%E5%B0%91%E6%95%B0%E6%8D%AE)
- [MySQL单表多大进行分库分表？](https://topjavaer.cn/database/mysql.html#mysql%E5%8D%95%E8%A1%A8%E5%A4%9A%E5%A4%A7%E8%BF%9B%E8%A1%8C%E5%88%86%E5%BA%93%E5%88%86%E8%A1%A8)
- [大表查询慢怎么优化？](https://topjavaer.cn/database/mysql.html#%E5%A4%A7%E8%A1%A8%E6%9F%A5%E8%AF%A2%E6%85%A2%E6%80%8E%E4%B9%88%E4%BC%98%E5%8C%96)
- [说说count()、count()和count()的区别](https://topjavaer.cn/database/mysql.html#%E8%AF%B4%E8%AF%B4count1count%E5%92%8Ccount%E5%AD%97%E6%AE%B5%E5%90%8D%E7%9A%84%E5%8C%BA%E5%88%AB)
- [MySQL中DATETIME 和 TIMESTAMP有什么区别？](https://topjavaer.cn/database/mysql.html#mysql%E4%B8%ADdatetime-%E5%92%8C-timestamp%E6%9C%89%E4%BB%80%E4%B9%88%E5%8C%BA%E5%88%AB)
- [说说为什么不建议用外键？](https://topjavaer.cn/database/mysql.html#%E8%AF%B4%E8%AF%B4%E4%B8%BA%E4%BB%80%E4%B9%88%E4%B8%8D%E5%BB%BA%E8%AE%AE%E7%94%A8%E5%A4%96%E9%94%AE)
- [使用自增主键有什么好处？](https://topjavaer.cn/database/mysql.html#%E4%BD%BF%E7%94%A8%E8%87%AA%E5%A2%9E%E4%B8%BB%E9%94%AE%E6%9C%89%E4%BB%80%E4%B9%88%E5%A5%BD%E5%A4%84)
- [自增主键保存在什么地方？](https://topjavaer.cn/database/mysql.html#%E8%87%AA%E5%A2%9E%E4%B8%BB%E9%94%AE%E4%BF%9D%E5%AD%98%E5%9C%A8%E4%BB%80%E4%B9%88%E5%9C%B0%E6%96%B9)
- [自增主键一定是连续的吗？](https://topjavaer.cn/database/mysql.html#%E8%87%AA%E5%A2%9E%E4%B8%BB%E9%94%AE%E4%B8%80%E5%AE%9A%E6%98%AF%E8%BF%9E%E7%BB%AD%E7%9A%84%E5%90%97)
- [InnoDB的自增值为什么不能回收利用？](https://topjavaer.cn/database/mysql.html#innodb%E7%9A%84%E8%87%AA%E5%A2%9E%E5%80%BC%E4%B8%BA%E4%BB%80%E4%B9%88%E4%B8%8D%E8%83%BD%E5%9B%9E%E6%94%B6%E5%88%A9%E7%94%A8)
- [MySQL数据如何同步到Redis缓存？](https://topjavaer.cn/database/mysql.html#mysql%E6%95%B0%E6%8D%AE%E5%A6%82%E4%BD%95%E5%90%8C%E6%AD%A5%E5%88%B0redis%E7%BC%93%E5%AD%98)