search
HomeDatabaseMysql Tutorialmysql tutorial: mysql create and delete index

Create and delete indexes
Index creation can be done in the CREATE TABLE statement, or you can use CREATE INDEX or ALTER TABLE alone to add indexes to the table. Dropping an index can be accomplished using the ALTER TABLE or DROP INDEX statement.
(1) Use the ALTER TABLE statement to create an index.
The syntax is as follows:
alter table table_name add index index_name (column_list);
alter table table_name add unique (column_list);
alter table table_name add primary key (column_list);
It includes 3 types: ordinary index, UNIQUE index and PRIMARY KEY index The format for creating an index. table_name is the name of the table to which the index is to be added. column_list indicates which columns to index. If there are multiple columns, separate them with commas. The index name index_name is optional. By default, MySQL will assign a name based on the first index column. Additionally, ALTER TABLE allows multiple tables to be altered in a single statement, so multiple indexes can be created simultaneously.
An example of creating an index is as follows:
mysql> use tpsc
Database changed
mysql> alter table tpsc add index shili (tpmc) ;
Query OK, 2 rows affected (0.08 sec)
Records: 2 Duplicates: 0 Warnings: 0
(2) Use the CREATE INDEX statement to add an index to the table.
Ability to add both normal index and UNIQUE index. The format is as follows:
create index index_name on table_name (column_list);
create unique index index_name on table_name (column_list);
Note: table_name, index_name and column_list have the same meaning as in the ALTER TABLE statement, and the index name is not optional. In addition, you cannot use the CREATE INDEX statement to create a PRIMARY KEY index.
(3) Delete index.
Deleting an index can be achieved using the ALTER TABLE or DROP INDEX statement. DROP INDEX can be processed as a statement inside ALTER TABLE, and its format is as follows:
drop index index_name on table_name;
alter table table_name drop index index_name;
alter table table_name drop primary key;
Among them, in the previous two statements, The index index_name in table_name is deleted. In the last statement, it is only used to delete the PRIMARY KEY index, because a table can only have one PRIMARY KEY index, so there is no need to specify the index name. If no PRIMARY KEY index is created, but the table has one or more UNIQUE indexes, MySQL drops the first UNIQUE index.
If a column is deleted from the table, the index will be affected. For a multi-column index, if one of the columns is deleted, the column will also be deleted from the index. If you delete all the columns that make up the index, the entire index will be deleted.
The operation of deleting the index, such as the following code:
mysql> drop index shili on tpsc;
Query OK, 2 rows affected (0.08 sec)
Records: 2 Duplicates: 0 Warnings: 0
This statement deletes the previously created name Index for "shili".

The above is the mysql tutorial: mysql creation and deletion of index content. For more related articles, please pay attention to the PHP Chinese website (www.php.cn)!


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
MySQL: An Introduction to the World's Most Popular DatabaseMySQL: An Introduction to the World's Most Popular DatabaseApr 12, 2025 am 12:18 AM

MySQL is an open source relational database management system, mainly used to store and retrieve data quickly and reliably. Its working principle includes client requests, query resolution, execution of queries and return results. Examples of usage include creating tables, inserting and querying data, and advanced features such as JOIN operations. Common errors involve SQL syntax, data types, and permissions, and optimization suggestions include the use of indexes, optimized queries, and partitioning of tables.

The Importance of MySQL: Data Storage and ManagementThe Importance of MySQL: Data Storage and ManagementApr 12, 2025 am 12:18 AM

MySQL is an open source relational database management system suitable for data storage, management, query and security. 1. It supports a variety of operating systems and is widely used in Web applications and other fields. 2. Through the client-server architecture and different storage engines, MySQL processes data efficiently. 3. Basic usage includes creating databases and tables, inserting, querying and updating data. 4. Advanced usage involves complex queries and stored procedures. 5. Common errors can be debugged through the EXPLAIN statement. 6. Performance optimization includes the rational use of indexes and optimized query statements.

Why Use MySQL? Benefits and AdvantagesWhy Use MySQL? Benefits and AdvantagesApr 12, 2025 am 12:17 AM

MySQL is chosen for its performance, reliability, ease of use, and community support. 1.MySQL provides efficient data storage and retrieval functions, supporting multiple data types and advanced query operations. 2. Adopt client-server architecture and multiple storage engines to support transaction and query optimization. 3. Easy to use, supports a variety of operating systems and programming languages. 4. Have strong community support and provide rich resources and solutions.

Describe InnoDB locking mechanisms (shared locks, exclusive locks, intention locks, record locks, gap locks, next-key locks).Describe InnoDB locking mechanisms (shared locks, exclusive locks, intention locks, record locks, gap locks, next-key locks).Apr 12, 2025 am 12:16 AM

InnoDB's lock mechanisms include shared locks, exclusive locks, intention locks, record locks, gap locks and next key locks. 1. Shared lock allows transactions to read data without preventing other transactions from reading. 2. Exclusive lock prevents other transactions from reading and modifying data. 3. Intention lock optimizes lock efficiency. 4. Record lock lock index record. 5. Gap lock locks index recording gap. 6. The next key lock is a combination of record lock and gap lock to ensure data consistency.

What are common causes of poor MySQL query performance?What are common causes of poor MySQL query performance?Apr 12, 2025 am 12:11 AM

The main reasons for poor MySQL query performance include not using indexes, wrong execution plan selection by the query optimizer, unreasonable table design, excessive data volume and lock competition. 1. No index causes slow querying, and adding indexes can significantly improve performance. 2. Use the EXPLAIN command to analyze the query plan and find out the optimizer error. 3. Reconstructing the table structure and optimizing JOIN conditions can improve table design problems. 4. When the data volume is large, partitioning and table division strategies are adopted. 5. In a high concurrency environment, optimizing transactions and locking strategies can reduce lock competition.

When should you use a composite index versus multiple single-column indexes?When should you use a composite index versus multiple single-column indexes?Apr 11, 2025 am 12:06 AM

In database optimization, indexing strategies should be selected according to query requirements: 1. When the query involves multiple columns and the order of conditions is fixed, use composite indexes; 2. When the query involves multiple columns but the order of conditions is not fixed, use multiple single-column indexes. Composite indexes are suitable for optimizing multi-column queries, while single-column indexes are suitable for single-column queries.

How to identify and optimize slow queries in MySQL? (slow query log, performance_schema)How to identify and optimize slow queries in MySQL? (slow query log, performance_schema)Apr 10, 2025 am 09:36 AM

To optimize MySQL slow query, slowquerylog and performance_schema need to be used: 1. Enable slowquerylog and set thresholds to record slow query; 2. Use performance_schema to analyze query execution details, find out performance bottlenecks and optimize.

MySQL and SQL: Essential Skills for DevelopersMySQL and SQL: Essential Skills for DevelopersApr 10, 2025 am 09:30 AM

MySQL and SQL are essential skills for developers. 1.MySQL is an open source relational database management system, and SQL is the standard language used to manage and operate databases. 2.MySQL supports multiple storage engines through efficient data storage and retrieval functions, and SQL completes complex data operations through simple statements. 3. Examples of usage include basic queries and advanced queries, such as filtering and sorting by condition. 4. Common errors include syntax errors and performance issues, which can be optimized by checking SQL statements and using EXPLAIN commands. 5. Performance optimization techniques include using indexes, avoiding full table scanning, optimizing JOIN operations and improving code readability.

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

AI Hentai Generator

AI Hentai Generator

Generate AI Hentai for free.

Hot Article

R.E.P.O. Energy Crystals Explained and What They Do (Yellow Crystal)
3 weeks agoBy尊渡假赌尊渡假赌尊渡假赌
R.E.P.O. Best Graphic Settings
3 weeks agoBy尊渡假赌尊渡假赌尊渡假赌
R.E.P.O. How to Fix Audio if You Can't Hear Anyone
3 weeks agoBy尊渡假赌尊渡假赌尊渡假赌
WWE 2K25: How To Unlock Everything In MyRise
3 weeks agoBy尊渡假赌尊渡假赌尊渡假赌

Hot Tools

WebStorm Mac version

WebStorm Mac version

Useful JavaScript development tools

Dreamweaver Mac version

Dreamweaver Mac version

Visual web development tools

PhpStorm Mac version

PhpStorm Mac version

The latest (2018.2.1) professional PHP integrated development tool

MantisBT

MantisBT

Mantis is an easy-to-deploy web-based defect tracking tool designed to aid in product defect tracking. It requires PHP, MySQL and a web server. Check out our demo and hosting services.

Zend Studio 13.0.1

Zend Studio 13.0.1

Powerful PHP integrated development environment