bitsCN.com
当在开发的时候有时候需要手动修复数据或者更新数据,一般在自己的项目里写一个main函数对数据读取或者修改即可,但执行的时候要从本地连接外网,
如果数据量很大的时候。几十万或者上百万等以上的话,性能会非常的差,这时候把sql语句写好放在数据库里直接执行会好很多。
在mysql数据库里的innodb引擎,一般数据增删改都有内置的事务的,而且有默认的超时限制,好像是50s,如果数据量大而且很多连接查询的话会超时,
这时候不妨把连接查询的数据创建临时表并对临时表创建索引,然后添加数据或修改数据对临时表进行连接关联,这时候性能会快很多,举个例子:
DROP TEMPORARY TABLE IF EXISTS tmp;
CREATE TEMPORARY TABLE tmp
select b.UserId,b.field1,b.field2, b.field3 from
(select Max(AutoId) as AutoId
from T_Table2 where UserId
group by UserId) a left join T_Table1 b on a.AutoId=b.AutoId;
ALTER TABLE tmp ADD INDEX `index_UserId` (`UserID` ASC) ;
INSERT INTO T_Table3(`UserId`,`field1`,`field2`,`field3`, `CreateTime`,`CreateIp`,`ModifyTime`,`ModifyIp`)
select a.UserId,a.field1,a.field2,a.field3,now(),'127.0.0.1',now(),'127.0.0.1'
from tmp;
临时表用完之后要删除,DROP TEMPORARY TABLE tmp;
bitsCN.com
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

The main role of MySQL in web applications is to store and manage data. 1.MySQL efficiently processes user information, product catalogs, transaction records and other data. 2. Through SQL query, developers can extract information from the database to generate dynamic content. 3.MySQL works based on the client-server model to ensure acceptable query speed.

The steps to build a MySQL database include: 1. Create a database and table, 2. Insert data, and 3. Conduct queries. First, use the CREATEDATABASE and CREATETABLE statements to create the database and table, then use the INSERTINTO statement to insert the data, and finally use the SELECT statement to query the data.

MySQL is suitable for beginners because it is easy to use and powerful. 1.MySQL is a relational database, and uses SQL for CRUD operations. 2. It is simple to install and requires the root user password to be configured. 3. Use INSERT, UPDATE, DELETE, and SELECT to perform data operations. 4. ORDERBY, WHERE and JOIN can be used for complex queries. 5. Debugging requires checking the syntax and use EXPLAIN to analyze the query. 6. Optimization suggestions include using indexes, choosing the right data type and good programming habits.


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

AI Hentai Generator
Generate AI Hentai for free.

Hot Article

Hot Tools

PhpStorm Mac version
The latest (2018.2.1) professional PHP integrated development tool

SublimeText3 Linux new version
SublimeText3 Linux latest version

VSCode Windows 64-bit Download
A free and powerful IDE editor launched by Microsoft

ZendStudio 13.5.1 Mac
Powerful PHP integrated development environment

Notepad++7.3.1
Easy-to-use and free code editor