前几天在客户现场做升级,脚本中move lob字段了,客户继续执行操作的时候,喊索引失效了。经查看,是非lob字段的索引失效,当时没注意,直接rebuild了,半夜回去的路上,经理问我,move lob字段,为什么其他索引会失效?我当时。。。夜深人静时,最佳思考时。思考的结果就是:我发现很多东西我都知道,但究其根本,就有点模糊了。比如:索引,我知道是根据rowid快速找到一行,但是,索引存储的是一列的值(单列索引),会不会存储与其他列的关系呢?。。。。
后来决定通过实验验证,不知道所以然,至少得知道依然呀。怎么着,先知道一个再说先。
--建测试表,含主键 create table dxmy_lob(id number primary key,name blob,sex varchar2(10),location varchar2(100)); select * from dba_lobs d where d.table_name = 'DXMY_LOB'; --插入数据 INSERT INTO DXMY_LOB VALUES(2,to_blob('110111011'),'MAN','SOMEWARE'); COMMIT; select * from dxmy_lob; --创建普通索引 create index ind_dxmy on dxmy_lob(sex); --move前查看索引状态 select d.owner,d.index_name,d.index_type,d.status,d.last_analyzed from dba_indexes d where d.table_name = 'DXMY_LOB'; OWNER INDEX_NAME INDEX_TYPE STATUS LAST_ANALYZED LM IND_DXMY NORMAL VALID 2015/12/17 4:29:51 LM SYS_C0011400 NORMAL VALID LM SYS_IL0000087754C00002$$ LOB VALID --move走起 alter table lm_lob move lob(name) store as LM_LOB_SEG (tablespace users); --move之后索引状态 select d.owner,d.index_name,d.index_type,d.status,d.last_analyzed from dba_indexes d where d.table_name = 'DXMY_LOB'; OWNER INDEX_NAME INDEX_TYPE STATUS LAST_ANALYZED LM IND_DXMY NORMAL VALID 2015/12/17 4:29:51 LM SYS_C0011400 NORMAL VALID LM SYS_IL0000087754C00002$$ LOB VALID 正常呀,莫非。。。

哎,我灵机一动,以为是复合索引,结果不能建。。
那最大的可能就是客户做了什么操作,是索引失效了。

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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