myisam innoDB是mysql常用的存储引擎
MyISAM不支持事务、也不支持外键,但其访问速度快,对事务完整性没有要求。
InnoDB存储引擎提供了具有提交、回滚和崩溃恢复能力的事务安全。但是比起MyISAM存储引擎,InnoDB写的处理效率差一些并且会占用更多的磁盘空间以保留数据和索引。
innodb的索引有两种,叫第一索引,以及第二索引。有的也叫聚集索引与辅助索引。其中聚集索引存放了表中的记录,查询的时候不需要回表扫描,同时索引项较大;辅助索引存放的位置信息,需要回表扫描,相对来说,I/0 次数会增加。
查询的时候最好能够从索引中取得数据,减少回表,相对来说离散的 I/0,
MYISAM 没有聚集索引。存放的记录的物理位置
OLTP (联机事务处理)故名思议主要强调事务,如(银行存款的修改,用户订单等)面向应用
OLAP (联机分析处理) 主要作为数据仓库,面向决策,分析等。
联接算法:
nested-loops join 主要思想是:从外表中拿出一个数据与内表的每一条数据比较,O(M*N) 。当有索引时:内表只需要比较索引的高度,近似于O(M*H)
Block nested--loops join 主要思想 是:改进 nested-loops join 外部表每次去一定的数据到缓冲区,比如10条,然后这10条记录在跟内部表的数据比较,减少内部表的扫描次数。
Hash join 只能== 以及!=,不能部分比较(为何?,hash是对整个字符串hash) 主要思想是:将外部表的数据放到join buffer,然后hash,这一阶段
为build;probe阶段,从内表中取出数据hash,比较。
基本的测试:
create TABLE myorder
( id int not null auto_increment,
userid int not null ,
orderdate date,
comein int DEFAULT 0,
comeout int DEFAULT 0,
PRIMARY key (id)
);
SELECT userid ,orderdate ,comein -comeout as rest
from myorder
GROUP BY userid ,orderdate;
create index myorderindex on myorder(id,userid);
explain SELECT userid ,orderdate ,comein -comeout as rest
from myorder
GROUP BY userid ,orderdate;

The main difference between MySQL and SQLite is the design concept and usage scenarios: 1. MySQL is suitable for large applications and enterprise-level solutions, supporting high performance and high concurrency; 2. SQLite is suitable for mobile applications and desktop software, lightweight and easy to embed.

Indexes in MySQL are an ordered structure of one or more columns in a database table, used to speed up data retrieval. 1) Indexes improve query speed by reducing the amount of scanned data. 2) B-Tree index uses a balanced tree structure, which is suitable for range query and sorting. 3) Use CREATEINDEX statements to create indexes, such as CREATEINDEXidx_customer_idONorders(customer_id). 4) Composite indexes can optimize multi-column queries, such as CREATEINDEXidx_customer_orderONorders(customer_id,order_date). 5) Use EXPLAIN to analyze query plans and avoid

Using transactions in MySQL ensures data consistency. 1) Start the transaction through STARTTRANSACTION, and then execute SQL operations and submit it with COMMIT or ROLLBACK. 2) Use SAVEPOINT to set a save point to allow partial rollback. 3) Performance optimization suggestions include shortening transaction time, avoiding large-scale queries and using isolation levels reasonably.

Scenarios where PostgreSQL is chosen instead of MySQL include: 1) complex queries and advanced SQL functions, 2) strict data integrity and ACID compliance, 3) advanced spatial functions are required, and 4) high performance is required when processing large data sets. PostgreSQL performs well in these aspects and is suitable for projects that require complex data processing and high data integrity.

The security of MySQL database can be achieved through the following measures: 1. User permission management: Strictly control access rights through CREATEUSER and GRANT commands. 2. Encrypted transmission: Configure SSL/TLS to ensure data transmission security. 3. Database backup and recovery: Use mysqldump or mysqlpump to regularly backup data. 4. Advanced security policy: Use a firewall to restrict access and enable audit logging operations. 5. Performance optimization and best practices: Take into account both safety and performance through indexing and query optimization and regular maintenance.

How to effectively monitor MySQL performance? Use tools such as mysqladmin, SHOWGLOBALSTATUS, PerconaMonitoring and Management (PMM), and MySQL EnterpriseMonitor. 1. Use mysqladmin to view the number of connections. 2. Use SHOWGLOBALSTATUS to view the query number. 3.PMM provides detailed performance data and graphical interface. 4.MySQLEnterpriseMonitor provides rich monitoring functions and alarm mechanisms.

The difference between MySQL and SQLServer is: 1) MySQL is open source and suitable for web and embedded systems, 2) SQLServer is a commercial product of Microsoft and is suitable for enterprise-level applications. There are significant differences between the two in storage engine, performance optimization and application scenarios. When choosing, you need to consider project size and future scalability.

In enterprise-level application scenarios that require high availability, advanced security and good integration, SQLServer should be chosen instead of MySQL. 1) SQLServer provides enterprise-level features such as high availability and advanced security. 2) It is closely integrated with Microsoft ecosystems such as VisualStudio and PowerBI. 3) SQLServer performs excellent in performance optimization and supports memory-optimized tables and column storage indexes.


Hot AI Tools

Undresser.AI Undress
AI-powered app for creating realistic nude photos

AI Clothes Remover
Online AI tool for removing clothes from photos.

Undress AI Tool
Undress images for free

Clothoff.io
AI clothes remover

Video Face Swap
Swap faces in any video effortlessly with our completely free AI face swap tool!

Hot Article

Hot Tools

Dreamweaver CS6
Visual web development tools

WebStorm Mac version
Useful JavaScript development tools

ZendStudio 13.5.1 Mac
Powerful PHP integrated development environment

SecLists
SecLists is the ultimate security tester's companion. It is a collection of various types of lists that are frequently used during security assessments, all in one place. SecLists helps make security testing more efficient and productive by conveniently providing all the lists a security tester might need. List types include usernames, passwords, URLs, fuzzing payloads, sensitive data patterns, web shells, and more. The tester can simply pull this repository onto a new test machine and he will have access to every type of list he needs.

SublimeText3 Mac version
God-level code editing software (SublimeText3)