Modify mysql table structure
For developers who use MySQL to develop, modifying the data table structure is an inevitable process. Changes to the data table structure may include adding new fields, deleting useless fields, modifying field data types or data lengths, etc. This article will introduce how to modify the MySQL table structure.
Modify the table name
You can modify the table name through the RENAME operation, as shown below:
ALTER TABLE old_table RENAME new_table;
Add a new column
You can use the ALTER TABLE statement The ADD keyword in to add a new column, as shown below:
ALTER TABLE table_name ADD new_column_name data_type;
Note: The "data_type" here refers to the data type of the new column, which can be int, varchar, etc.
Delete columns
You can use the DROP keyword in the ALTER TABLE statement to delete columns, as shown below:
ALTER TABLE table_name DROP column_name;
Note: Deleting a column will affect the data in the table, Please proceed with caution.
Modify columns
You can use the MODIFY keyword in the ALTER TABLE statement to modify the data type and length of the column, as shown below:
ALTER TABLE table_name MODIFY column_name new_data_type(new_length);
Note: Modify the data of the column Type and length will also affect the data in the table, please proceed with caution.
Modify the column name
You can use the CHANGE keyword in the ALTER TABLE statement to modify the column name, as shown below:
ALTER TABLE table_name CHANGE old_column_name new_column_name data_type;
Modify the column position
You can use the FIRST and AFTER keywords in the ALTER TABLE statement to modify the position of the columns, as shown below:
ALTER TABLE table_name MODIFY column_name data_type FIRST; ALTER TABLE table_name MODIFY column_name data_type AFTER another_column_name;
Note: If you use the FIRST keyword, the column will be moved to the first column, if you use the AFTER key word, the column will be moved after another column.
Modify the primary key
You can use the ADD and DROP keywords in the ALTER TABLE statement to add or delete the primary key, as shown below:
ALTER TABLE table_name ADD PRIMARY KEY (column_name); ALTER TABLE table_name DROP PRIMARY KEY;
Modify the unique key
You can use the ADD and DROP keywords in the ALTER TABLE statement to add or delete unique keys, as follows:
ALTER TABLE table_name ADD UNIQUE (column_name); ALTER TABLE table_name DROP INDEX unique_index_name;
Note: If you use the ADD keyword to add a unique key, you need to name the unique key.
Modify index
You can use the ADD, DROP and RENAME keywords in the ALTER TABLE statement to add, delete or rename indexes, as follows:
ALTER TABLE table_name ADD INDEX index_name (column_name); ALTER TABLE table_name DROP INDEX index_name; ALTER TABLE table_name RENAME INDEX old_index_name TO new_index_name;
Note: If you use the ADD keyword to add an index, you need to give the index a name.
Modify the self-growing column
You can use the AUTO_INCREMENT keyword in the ALTER TABLE statement to modify the starting value of the self-growing column, as follows:
ALTER TABLE table_name AUTO_INCREMENT = 100;
Modify the storage engine
You can use the ENGINE keyword in the ALTER TABLE statement to modify the storage engine, as shown below:
ALTER TABLE table_name ENGINE=InnoDB;
Note: Different storage engines support different functions and performance, and you need to be careful when switching storage engines. .
In short, modifying the MySQL table structure can be achieved through the ALTER TABLE statement, but it should be noted that the modification may have an impact on the data in the table. Please back up the data before operating.
The above is the detailed content of Modify mysql table structure. For more information, please follow other related articles on the PHP Chinese website!

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

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

Hot Article

Hot Tools

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

SublimeText3 Chinese version
Chinese version, very easy to use

Zend Studio 13.0.1
Powerful PHP integrated development environment

Dreamweaver CS6
Visual web development tools

SublimeText3 Mac version
God-level code editing software (SublimeText3)

Hot Topics

Full table scanning may be faster in MySQL than using indexes. Specific cases include: 1) the data volume is small; 2) when the query returns a large amount of data; 3) when the index column is not highly selective; 4) when the complex query. By analyzing query plans, optimizing indexes, avoiding over-index and regularly maintaining tables, you can make the best choices in practical applications.

Yes, MySQL can be installed on Windows 7, and although Microsoft has stopped supporting Windows 7, MySQL is still compatible with it. However, the following points should be noted during the installation process: Download the MySQL installer for Windows. Select the appropriate version of MySQL (community or enterprise). Select the appropriate installation directory and character set during the installation process. Set the root user password and keep it properly. Connect to the database for testing. Note the compatibility and security issues on Windows 7, and it is recommended to upgrade to a supported operating system.

InnoDB's full-text search capabilities are very powerful, which can significantly improve database query efficiency and ability to process large amounts of text data. 1) InnoDB implements full-text search through inverted indexing, supporting basic and advanced search queries. 2) Use MATCH and AGAINST keywords to search, support Boolean mode and phrase search. 3) Optimization methods include using word segmentation technology, periodic rebuilding of indexes and adjusting cache size to improve performance and accuracy.

The difference between clustered index and non-clustered index is: 1. Clustered index stores data rows in the index structure, which is suitable for querying by primary key and range. 2. The non-clustered index stores index key values and pointers to data rows, and is suitable for non-primary key column queries.

MySQL is an open source relational database management system. 1) Create database and tables: Use the CREATEDATABASE and CREATETABLE commands. 2) Basic operations: INSERT, UPDATE, DELETE and SELECT. 3) Advanced operations: JOIN, subquery and transaction processing. 4) Debugging skills: Check syntax, data type and permissions. 5) Optimization suggestions: Use indexes, avoid SELECT* and use transactions.

In MySQL database, the relationship between the user and the database is defined by permissions and tables. The user has a username and password to access the database. Permissions are granted through the GRANT command, while the table is created by the CREATE TABLE command. To establish a relationship between a user and a database, you need to create a database, create a user, and then grant permissions.

MySQL supports four index types: B-Tree, Hash, Full-text, and Spatial. 1.B-Tree index is suitable for equal value search, range query and sorting. 2. Hash index is suitable for equal value searches, but does not support range query and sorting. 3. Full-text index is used for full-text search and is suitable for processing large amounts of text data. 4. Spatial index is used for geospatial data query and is suitable for GIS applications.

MySQL and MariaDB can coexist, but need to be configured with caution. The key is to allocate different port numbers and data directories to each database, and adjust parameters such as memory allocation and cache size. Connection pooling, application configuration, and version differences also need to be considered and need to be carefully tested and planned to avoid pitfalls. Running two databases simultaneously can cause performance problems in situations where resources are limited.
