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bitsCN.com索引的目的是大大提高查询效率,还有读写效率。
kettle向sql里面插入,更新时,也要建立索引,可以大大提升处理时间。
但是建立索引报错:Specified key was too long; max key length is 1000 bytes
这是mysql中,索引字段的类型设置的总体过长,看一下fields里面字段类型,总体加起来不超过1000字节
注意,字段长度,是char长度乘以自身字段类型的位数,累加和不能超过限定的key长1000:
latin1 = 1 byte = 1 character
uft8 = 3 byte = 1 character
gbk = 2 byte = 1 character
以GBK为例:
CREATE UNIQUE INDEX `unique_record` ON reports (`report_name`, `report_client`, `report_city`);
其中report_name varchar(200), report_client varchar(200), report_city varchar(200)
(200 + 200 +200) * 2 = 1200 > 1000,就会报1071错误,只要将report_city改为varchar(100)那么索引就能成功建立。
但如果表是UTF8字符集,那索引还是建立不了,因此要乘以3。
KEY `idx_1` (`packagename`,`storename`,`app_name`,`version`,`category`,`app_link_hash`) USING BTREE
字段类型都是utf8,乘3后,超过1000。
我建的表,字段长度超了,而数据不能动,所以就用了一下小技巧:
1,applink字段要200以上,用了必超。解决办法:将applink用MD5算法,转换为特定长度的applink_hash码(32位长),一一对应,长度特定,用这个新字段只有32位就行了。排除过长字段,转换成特定hashcode,一一对应。
2,kettle插入时分析唯一key。字段之间关系,很多字段联合起来可以唯一确定某个字段,那这个字段就不用出现在索引中。kettle插入时就不用去比对这个字段
3,改成小字段的兼容类型。如果字段内容,允许,也就是包含的内容,很少,比如utf8的类型,可以修改成gbk,就可以省去一个字段。但是数据内容必须能被gbk包含,否则,内容不识别,插进去也没用。
bitsCN.com
InnoDBBufferPool reduces disk I/O by caching data and indexing pages, improving database performance. Its working principle includes: 1. Data reading: Read data from BufferPool; 2. Data writing: After modifying the data, write to BufferPool and refresh it to disk regularly; 3. Cache management: Use the LRU algorithm to manage cache pages; 4. Reading mechanism: Load adjacent data pages in advance. By sizing the BufferPool and using multiple instances, database performance can be optimized.

Compared with other programming languages, MySQL is mainly used to store and manage data, while other languages such as Python, Java, and C are used for logical processing and application development. MySQL is known for its high performance, scalability and cross-platform support, suitable for data management needs, while other languages have advantages in their respective fields such as data analytics, enterprise applications, and system programming.

MySQL is worth learning because it is a powerful open source database management system suitable for data storage, management and analysis. 1) MySQL is a relational database that uses SQL to operate data and is suitable for structured data management. 2) The SQL language is the key to interacting with MySQL and supports CRUD operations. 3) The working principle of MySQL includes client/server architecture, storage engine and query optimizer. 4) Basic usage includes creating databases and tables, and advanced usage involves joining tables using JOIN. 5) Common errors include syntax errors and permission issues, and debugging skills include checking syntax and using EXPLAIN commands. 6) Performance optimization involves the use of indexes, optimization of SQL statements and regular maintenance of databases.

MySQL is suitable for beginners to learn database skills. 1. Install MySQL server and client tools. 2. Understand basic SQL queries, such as SELECT. 3. Master data operations: create tables, insert, update, and delete data. 4. Learn advanced skills: subquery and window functions. 5. Debugging and optimization: Check syntax, use indexes, avoid SELECT*, and use LIMIT.

MySQL efficiently manages structured data through table structure and SQL query, and implements inter-table relationships through foreign keys. 1. Define the data format and type when creating a table. 2. Use foreign keys to establish relationships between tables. 3. Improve performance through indexing and query optimization. 4. Regularly backup and monitor databases to ensure data security and performance optimization.

MySQL is an open source relational database management system that is widely used in Web development. Its key features include: 1. Supports multiple storage engines, such as InnoDB and MyISAM, suitable for different scenarios; 2. Provides master-slave replication functions to facilitate load balancing and data backup; 3. Improve query efficiency through query optimization and index use.

SQL is used to interact with MySQL database to realize data addition, deletion, modification, inspection and database design. 1) SQL performs data operations through SELECT, INSERT, UPDATE, DELETE statements; 2) Use CREATE, ALTER, DROP statements for database design and management; 3) Complex queries and data analysis are implemented through SQL to improve business decision-making efficiency.

The basic operations of MySQL include creating databases, tables, and using SQL to perform CRUD operations on data. 1. Create a database: CREATEDATABASEmy_first_db; 2. Create a table: CREATETABLEbooks(idINTAUTO_INCREMENTPRIMARYKEY, titleVARCHAR(100)NOTNULL, authorVARCHAR(100)NOTNULL, published_yearINT); 3. Insert data: INSERTINTObooks(title, author, published_year)VA


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