search
HomeDatabaseMysql TutorialMysql 自动增加设定基值的语句_MySQL

bitsCN.com 核心代码:

ALTER TABLE 表名 AUTO_INCREMENT = 设定的值

MySQL ALTER语法中ALTER [IGNORE] TABLE tbl_name alter_spec [, alter_spec ...]

alter_specification:
ADD [COLUMN] create_definition [FIRST | AFTER column_name ]
or ADD INDEX [index_name] (index_col_name,...)
or ADD PRIMARY KEY (index_col_name,...)
or ADD UNIQUE [index_name] (index_col_name,...)
or ALTER [COLUMN] col_name {SET DEFAULT literal | DROP DEFAULT}
or CHANGE [COLUMN] old_col_name create_definition
or MODIFY [COLUMN] create_definition
or DROP [COLUMN] col_name
or DROP PRIMARY KEY
or DROP INDEX index_name
or RENAME [AS] new_tbl_name
or table_options
eg:
mysql> alter table topics change hotico hot_count int(4);
mysql> alter table topics alter hot_count set default 1;

补充:
加索引
mysql> alter table 表名 add index 索引名 (字段名1[,字段名2 …]);

例子: mysql> alter table employee add index emp_name (name);
加主关键字的索引
mysql> alter table 表名 add primary key (字段名);
例子: mysql> alter table employee add primary key(id);
加唯一限制条件的索引
mysql> alter table 表名 add unique 索引名 (字段名);
例子: mysql> alter table employee add unique emp_name2(cardnumber);
MySQL ALTER语法运用:查看某个表的索引
mysql> show index from 表名;

例子: mysql> show index from employee;

删除某个索引
mysql> alter table 表名 drop index 索引名;

例子: mysql>alter table employee drop index emp_name;

修改表:增加字段:mysql> ALTER TABLE table_name ADD field_name field_type;
查看表:mysql> SELECT * FROM table_name;

修改原字段名称及类型:mysql> ALTER TABLE table_name CHANGE old_field_name new_field_name field_type;

删除字段:MySQL ALTER TABLE table_name DROP field_name;bitsCN.com

Statement
The content of this article is voluntarily contributed by netizens, and the copyright belongs to the original author. This site does not assume corresponding legal responsibility. If you find any content suspected of plagiarism or infringement, please contact admin@php.cn
How does MySQL's licensing compare to other database systems?How does MySQL's licensing compare to other database systems?Apr 25, 2025 am 12:26 AM

MySQL uses a GPL license. 1) The GPL license allows the free use, modification and distribution of MySQL, but the modified distribution must comply with GPL. 2) Commercial licenses can avoid public modifications and are suitable for commercial applications that require confidentiality.

When would you choose InnoDB over MyISAM, and vice versa?When would you choose InnoDB over MyISAM, and vice versa?Apr 25, 2025 am 12:22 AM

The situations when choosing InnoDB instead of MyISAM include: 1) transaction support, 2) high concurrency environment, 3) high data consistency; conversely, the situation when choosing MyISAM includes: 1) mainly read operations, 2) no transaction support is required. InnoDB is suitable for applications that require high data consistency and transaction processing, such as e-commerce platforms, while MyISAM is suitable for read-intensive and transaction-free applications such as blog systems.

Explain the purpose of foreign keys in MySQL.Explain the purpose of foreign keys in MySQL.Apr 25, 2025 am 12:17 AM

In MySQL, the function of foreign keys is to establish the relationship between tables and ensure the consistency and integrity of the data. Foreign keys maintain the effectiveness of data through reference integrity checks and cascading operations. Pay attention to performance optimization and avoid common errors when using them.

What are the different types of indexes in MySQL?What are the different types of indexes in MySQL?Apr 25, 2025 am 12:12 AM

There are four main index types in MySQL: B-Tree index, hash index, full-text index and spatial index. 1.B-Tree index is suitable for range query, sorting and grouping, and is suitable for creation on the name column of the employees table. 2. Hash index is suitable for equivalent queries and is suitable for creation on the id column of the hash_table table of the MEMORY storage engine. 3. Full text index is used for text search, suitable for creation on the content column of the articles table. 4. Spatial index is used for geospatial query, suitable for creation on geom columns of locations table.

How do you create an index in MySQL?How do you create an index in MySQL?Apr 25, 2025 am 12:06 AM

TocreateanindexinMySQL,usetheCREATEINDEXstatement.1)Forasinglecolumn,use"CREATEINDEXidx_lastnameONemployees(lastname);"2)Foracompositeindex,use"CREATEINDEXidx_nameONemployees(lastname,firstname);"3)Forauniqueindex,use"CREATEU

How does MySQL differ from SQLite?How does MySQL differ from SQLite?Apr 24, 2025 am 12:12 AM

The main difference between MySQL and SQLite is the design concept and usage scenarios: 1. MySQL is suitable for large applications and enterprise-level solutions, supporting high performance and high concurrency; 2. SQLite is suitable for mobile applications and desktop software, lightweight and easy to embed.

What are indexes in MySQL, and how do they improve performance?What are indexes in MySQL, and how do they improve performance?Apr 24, 2025 am 12:09 AM

Indexes in MySQL are an ordered structure of one or more columns in a database table, used to speed up data retrieval. 1) Indexes improve query speed by reducing the amount of scanned data. 2) B-Tree index uses a balanced tree structure, which is suitable for range query and sorting. 3) Use CREATEINDEX statements to create indexes, such as CREATEINDEXidx_customer_idONorders(customer_id). 4) Composite indexes can optimize multi-column queries, such as CREATEINDEXidx_customer_orderONorders(customer_id,order_date). 5) Use EXPLAIN to analyze query plans and avoid

Explain how to use transactions in MySQL to ensure data consistency.Explain how to use transactions in MySQL to ensure data consistency.Apr 24, 2025 am 12:09 AM

Using transactions in MySQL ensures data consistency. 1) Start the transaction through STARTTRANSACTION, and then execute SQL operations and submit it with COMMIT or ROLLBACK. 2) Use SAVEPOINT to set a save point to allow partial rollback. 3) Performance optimization suggestions include shortening transaction time, avoiding large-scale queries and using isolation levels reasonably.

See all articles

Hot AI Tools

Undresser.AI Undress

Undresser.AI Undress

AI-powered app for creating realistic nude photos

AI Clothes Remover

AI Clothes Remover

Online AI tool for removing clothes from photos.

Undress AI Tool

Undress AI Tool

Undress images for free

Clothoff.io

Clothoff.io

AI clothes remover

Video Face Swap

Video Face Swap

Swap faces in any video effortlessly with our completely free AI face swap tool!

Hot Tools

PhpStorm Mac version

PhpStorm Mac version

The latest (2018.2.1) professional PHP integrated development tool

Notepad++7.3.1

Notepad++7.3.1

Easy-to-use and free code editor

SublimeText3 Linux new version

SublimeText3 Linux new version

SublimeText3 Linux latest version

mPDF

mPDF

mPDF is a PHP library that can generate PDF files from UTF-8 encoded HTML. The original author, Ian Back, wrote mPDF to output PDF files "on the fly" from his website and handle different languages. It is slower than original scripts like HTML2FPDF and produces larger files when using Unicode fonts, but supports CSS styles etc. and has a lot of enhancements. Supports almost all languages, including RTL (Arabic and Hebrew) and CJK (Chinese, Japanese and Korean). Supports nested block-level elements (such as P, DIV),

SAP NetWeaver Server Adapter for Eclipse

SAP NetWeaver Server Adapter for Eclipse

Integrate Eclipse with SAP NetWeaver application server.