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mysql数据库学习——3,表的创建,删除和变更
表创建create table mytbl(id int auto_increment not null,name char(10) not null,birth date not null,wight int,sex enum('f','m'));指定数据库引擎的表创建create table mytbl(id int auto_increment not null,name char(10) not null,birth date not null,wight int,sex enum('f','m'))engine=memory;创建临时表create temporary table mytbl(id int auto_increment not null,name char(10) not null,birth date not null,wight int,sex enum('f','m'));
复制数据表结构(也可以这样创建一个临时表作副本create temporary table tblnew like tblold)create table tblnew like tblold同时复制数据insert into tblnew select * from tblold从查询结果创建表create table tblnew select * from tblold
删除数据表
drop table tbl_namedrop table tbl_name ,tbl2_namedrop table if exists tbl_namedrop temporary table tbl_name
修改数据表
修改数据列的数据类型alter table mytbl modify i mediumint unsignedalter table mytbl chang i i mediumint unsigned修改数据列的数据类型和字符集alter table mytbl modify i mediumint character set ucs2修改数据表的存储引擎alter table mytbl engine=engine_name
重命名数据表alter table tbl_name rename to new_tbl_namerename talbe tbl_name to new_tbl_name重命名多个数据表 rename talbe tbl_name to new_tbl_name,t1 to t2 ,t3 to t4移动数据表到另一个数据库alter table db1.tbl_name rename to db2.new_tbl_namerename talbe db1.tbl_name to db2.new_tbl_name
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MySQL processes data replication through three modes: asynchronous, semi-synchronous and group replication. 1) Asynchronous replication performance is high but data may be lost. 2) Semi-synchronous replication improves data security but increases latency. 3) Group replication supports multi-master replication and failover, suitable for high availability requirements.

The EXPLAIN statement can be used to analyze and improve SQL query performance. 1. Execute the EXPLAIN statement to view the query plan. 2. Analyze the output results, pay attention to access type, index usage and JOIN order. 3. Create or adjust indexes based on the analysis results, optimize JOIN operations, and avoid full table scanning to improve query efficiency.

Using mysqldump for logical backup and MySQLEnterpriseBackup for hot backup are effective ways to back up MySQL databases. 1. Use mysqldump to back up the database: mysqldump-uroot-pmydatabase>mydatabase_backup.sql. 2. Use MySQLEnterpriseBackup for hot backup: mysqlbackup--user=root-password=password--backup-dir=/path/to/backupbackup. When recovering, use the corresponding life

The main reasons for slow MySQL query include missing or improper use of indexes, query complexity, excessive data volume and insufficient hardware resources. Optimization suggestions include: 1. Create appropriate indexes; 2. Optimize query statements; 3. Use table partitioning technology; 4. Appropriately upgrade hardware.

MySQL view is a virtual table based on SQL query results and does not store data. 1) Views simplify complex queries, 2) Enhance data security, and 3) Maintain data consistency. Views are stored queries in databases that can be used like tables, but data is generated dynamically.

MySQLdiffersfromotherSQLdialectsinsyntaxforLIMIT,auto-increment,stringcomparison,subqueries,andperformanceanalysis.1)MySQLusesLIMIT,whileSQLServerusesTOPandOracleusesROWNUM.2)MySQL'sAUTO_INCREMENTcontrastswithPostgreSQL'sSERIALandOracle'ssequenceandt

MySQL partitioning improves performance and simplifies maintenance. 1) Divide large tables into small pieces by specific criteria (such as date ranges), 2) physically divide data into independent files, 3) MySQL can focus on related partitions when querying, 4) Query optimizer can skip unrelated partitions, 5) Choosing the right partition strategy and maintaining it regularly is key.

How to grant and revoke permissions in MySQL? 1. Use the GRANT statement to grant permissions, such as GRANTALLPRIVILEGESONdatabase_name.TO'username'@'host'; 2. Use the REVOKE statement to revoke permissions, such as REVOKEALLPRIVILEGESONdatabase_name.FROM'username'@'host' to ensure timely communication of permission changes.


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