通常可以索引开始的几个字符,而不是全部值,以节约空间并得到好的性能。这使索引需要的空间变小,但是也会降低选择性。索引选择
有时需要索引很长的字符列,它会使索引变大而且变慢。一个策略就是模拟哈希索引。但是有时这也不够好,那?
通常可以索引开始的几个字符,而不是全部值,以节约空间并得到好的性能。这使索引需要的空间变小,但是也会降低选择性。索引选择性是不重复的索引值和表中所有行的比值。高选择性的索引有好处,因为它使mysql在查找匹配的时候可以过波掉更多的行。唯一索引的选择率为1,为最佳值。
如果索引BLOG和TEXT列,,或者很长的varchar列,就必须定义前缀索引,因为mysql不允许索引它们的全文化。
可以在同一个查询中针对许多不同的前缀长度进行计算,选择选择性好的。 【Linux公社 】
(用LEFT函数,left(city,4))
添加前缀索引
mysql>alter table test.test add key (city(7));
前缀索引能很好地减少索引的大小及提高速度,但是mysql不能在order by 和group by查询中使用前缀索引,也不能把它们用伯覆盖索引。
有时后缀索引也挺有用,例如查找某个域名的所有电子邮件地址。mysql不支持反向索引,但是可以把反向字符串保存起来,并且索引它的前缀。可以用触发器维护这种索引。

In database optimization, indexing strategies should be selected according to query requirements: 1. When the query involves multiple columns and the order of conditions is fixed, use composite indexes; 2. When the query involves multiple columns but the order of conditions is not fixed, use multiple single-column indexes. Composite indexes are suitable for optimizing multi-column queries, while single-column indexes are suitable for single-column queries.

To optimize MySQL slow query, slowquerylog and performance_schema need to be used: 1. Enable slowquerylog and set thresholds to record slow query; 2. Use performance_schema to analyze query execution details, find out performance bottlenecks and optimize.

MySQL and SQL are essential skills for developers. 1.MySQL is an open source relational database management system, and SQL is the standard language used to manage and operate databases. 2.MySQL supports multiple storage engines through efficient data storage and retrieval functions, and SQL completes complex data operations through simple statements. 3. Examples of usage include basic queries and advanced queries, such as filtering and sorting by condition. 4. Common errors include syntax errors and performance issues, which can be optimized by checking SQL statements and using EXPLAIN commands. 5. Performance optimization techniques include using indexes, avoiding full table scanning, optimizing JOIN operations and improving code readability.

MySQL asynchronous master-slave replication enables data synchronization through binlog, improving read performance and high availability. 1) The master server record changes to binlog; 2) The slave server reads binlog through I/O threads; 3) The server SQL thread applies binlog to synchronize data.

MySQL is an open source relational database management system. 1) Create database and tables: Use the CREATEDATABASE and CREATETABLE commands. 2) Basic operations: INSERT, UPDATE, DELETE and SELECT. 3) Advanced operations: JOIN, subquery and transaction processing. 4) Debugging skills: Check syntax, data type and permissions. 5) Optimization suggestions: Use indexes, avoid SELECT* and use transactions.

The installation and basic operations of MySQL include: 1. Download and install MySQL, set the root user password; 2. Use SQL commands to create databases and tables, such as CREATEDATABASE and CREATETABLE; 3. Execute CRUD operations, use INSERT, SELECT, UPDATE, DELETE commands; 4. Create indexes and stored procedures to optimize performance and implement complex logic. With these steps, you can build and manage MySQL databases from scratch.

InnoDBBufferPool improves the performance of MySQL databases by loading data and index pages into memory. 1) The data page is loaded into the BufferPool to reduce disk I/O. 2) Dirty pages are marked and refreshed to disk regularly. 3) LRU algorithm management data page elimination. 4) The read-out mechanism loads the possible data pages in advance.

MySQL is suitable for beginners because it is simple to install, powerful and easy to manage data. 1. Simple installation and configuration, suitable for a variety of operating systems. 2. Support basic operations such as creating databases and tables, inserting, querying, updating and deleting data. 3. Provide advanced functions such as JOIN operations and subqueries. 4. Performance can be improved through indexing, query optimization and table partitioning. 5. Support backup, recovery and security measures to ensure data security and consistency.


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