How to add columns (fields) to a table in mysql?
Mysql method to add columns to a table: 1. Use "ALTER TABLE table name ADD new field name data type [constraints];" to add columns at the end; 2. Use "ALTER TABLE table name ADD new Field Name Data Type [Constraint] FIRST;" Add columns at the beginning.
(Recommended tutorial: mysql video tutorial)
MySQL data table is composed of rows and columns, usually The "columns" of the table are called fields, and the "rows" of the table are called records. As your business changes, you may need to add new fields to existing tables.
MySQL allows adding fields at the beginning, middle and end.
Add fields at the end
A complete field includes field name, data type and constraints. The syntax format for adding fields in MySQL is as follows:
ALTER TABLE <表名> ADD <新字段名><数据类型>[约束条件];
The syntax format is explained as follows:
is the name of the data table;
is the name of the field to be added; is the field that can store data Data type;
[Constraints] is optional and is used to constrain the added fields.
This syntax format adds a new field at the last position of the table (after the last column) by default.
Note: In this section we only add new fields and do not pay attention to its constraints.
Example 1
Create a new student data table in the test database. The SQL statements and running results are as follows:
mysql> USE test; Database changed mysql> CREATE TABLE student ( -> id INT(4), -> name VARCHAR(20), -> sex CHAR(1)); Query OK, 0 rows affected (0.09 sec)Copy after loginUse DESC to view students The table structure, SQL statements and running results are as follows:
mysql> DESC student; +-------+-------------+------+-----+---------+-------+ | Field | Type | Null | Key | Default | Extra | +-------+-------------+------+-----+---------+-------+ | id | int(4) | YES | | NULL | | | name | varchar(20) | YES | | NULL | | | sex | char(1) | YES | | NULL | | +-------+-------------+------+-----+---------+-------+ 3 rows in set (0.01 sec)
Copy after loginUse the ALTER TABLE statement to add an INT type field age, the SQL statements and running results are as follows:
mysql> ALTER TABLE student ADD age INT(4); Query OK, 0 rows affected (0.16 sec) Records: 0 Duplicates: 0 Warnings: 0
Copy after loginUse DESC to view the student table structure, Verify whether the age field is added successfully. The SQL statement and running results are as follows:
mysql> DESC student; +-------+-------------+------+-----+---------+-------+ | Field | Type | Null | Key | Default | Extra | +-------+-------------+------+-----+---------+-------+ | id | int(4) | YES | | NULL | | | name | varchar(20) | YES | | NULL | | | sex | char(1) | YES | | NULL | | | age | int(4) | YES | | NULL | | +-------+-------------+------+-----+---------+-------+ 4 rows in set (0.00 sec)
Copy after loginAs you can see from the running results, the age field has been added to the student table, and the field is at the last position of the table. The field was added successfully.
Add fields at the beginning
MySQL defaults to adding a new field at the last position of the table. If you want to add a new field at the beginning (before the first column ) to add a new field, you can use the FIRST keyword, the syntax format is as follows:
ALTER TABLE <表名> ADD <新字段名> <数据类型> [约束条件] FIRST;
Copy after loginThe FIRST keyword is generally placed at the end of the statement.
Example 2
Use the ALTER TABLE statement to add the INT type field stuId in the first column of the table. The SQL statement and running results are as follows.
mysql> ALTER TABLE student ADD stuId INT(4) FIRST; Query OK, 0 rows affected (0.14 sec) Records: 0 Duplicates: 0 Warnings: 0 mysql> DESC student; +-------+-------------+------+-----+---------+-------+ | Field | Type | Null | Key | Default | Extra | +-------+-------------+------+-----+---------+-------+ | stuId | int(4) | YES | | NULL | | | id | int(4) | YES | | NULL | | | name | varchar(20) | YES | | NULL | | | sex | char(1) | YES | | NULL | | | age | int(4) | YES | | NULL | | +-------+-------------+------+-----+---------+-------+ 5 rows in set (0.00 sec)
Copy after loginYou can see from the running results that the stuId field has been added to the student table, and the field is at the first position in the table. The field was added successfully.
Add fields in the middle
In addition to allowing fields to be added at the beginning and end of the table, MySQL also allows fields to be added in the middle ( After the specified field), you need to use the AFTER keyword. The syntax format is as follows:
ALTER TABLE <表名> ADD <新字段名> <数据类型> [约束条件] AFTER <已经存在的字段名>;
Copy after loginThe function of AFTER is to add a new field after an existing field.
Note that you can only add a new field after an existing field, but not in front of it.
Example 3
Use the ALTER TABLE statement to add a field named stuno with data type INT in the student table. The stuno field is located after the name field. The SQL statement and running results are as follows:
mysql> ALTER TABLE student ADD stuno INT(11) AFTER name; Query OK, 0 rows affected (0.13 sec) Records: 0 Duplicates: 0 Warnings: 0 mysql> DESC student; +-------+-------------+------+-----+---------+-------+ | Field | Type | Null | Key | Default | Extra | +-------+-------------+------+-----+---------+-------+ | stuId | int(4) | YES | | NULL | | | id | int(4) | YES | | NULL | | | name | varchar(20) | YES | | NULL | | | stuno | int(11) | YES | | NULL | | | sex | char(1) | YES | | NULL | | | age | int(4) | YES | | NULL | | +-------+-------------+------+-----+---------+-------+ 6 rows in set (0.00 sec)
Copy after loginAs can be seen from the running results, the stuId field has been added to the student table, and the field is located behind the name field. The field was added successfully.
Related recommendations: php training
The above is the detailed content of How to add columns (fields) to a table in mysql?. For more information, please follow other related articles on the PHP Chinese website!
Statement of this WebsiteThe 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
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
R.E.P.O. Energy Crystals Explained and What They Do (Yellow Crystal)2 weeks ago By 尊渡假赌尊渡假赌尊渡假赌Hello Kitty Island Adventure: How To Get Giant Seeds1 months ago By 尊渡假赌尊渡假赌尊渡假赌How Long Does It Take To Beat Split Fiction?4 weeks ago By DDDR.E.P.O. Save File Location: Where Is It & How to Protect It?4 weeks ago By DDDTwo Point Museum: All Exhibits And Where To Find Them1 months ago By 尊渡假赌尊渡假赌尊渡假赌
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
See all articles
PHP's big data structure processing skills
May 08, 2024 am 10:24 AM
Big data structure processing skills: Chunking: Break down the data set and process it in chunks to reduce memory consumption. Generator: Generate data items one by one without loading the entire data set, suitable for unlimited data sets. Streaming: Read files or query results line by line, suitable for large files or remote data. External storage: For very large data sets, store the data in a database or NoSQL.
How to use MySQL backup and restore in PHP?
Jun 03, 2024 pm 12:19 PM
Backing up and restoring a MySQL database in PHP can be achieved by following these steps: Back up the database: Use the mysqldump command to dump the database into a SQL file. Restore database: Use the mysql command to restore the database from SQL files.
How to optimize MySQL query performance in PHP?
Jun 03, 2024 pm 08:11 PM
MySQL query performance can be optimized by building indexes that reduce lookup time from linear complexity to logarithmic complexity. Use PreparedStatements to prevent SQL injection and improve query performance. Limit query results and reduce the amount of data processed by the server. Optimize join queries, including using appropriate join types, creating indexes, and considering using subqueries. Analyze queries to identify bottlenecks; use caching to reduce database load; optimize PHP code to minimize overhead.
How to insert data into a MySQL table using PHP?
Jun 02, 2024 pm 02:26 PM
How to insert data into MySQL table? Connect to the database: Use mysqli to establish a connection to the database. Prepare the SQL query: Write an INSERT statement to specify the columns and values to be inserted. Execute query: Use the query() method to execute the insertion query. If successful, a confirmation message will be output.
How to create a MySQL table using PHP?
Jun 04, 2024 pm 01:57 PM
Creating a MySQL table using PHP requires the following steps: Connect to the database. Create the database if it does not exist. Select a database. Create table. Execute the query. Close the connection.
How to use MySQL stored procedures in PHP?
Jun 02, 2024 pm 02:13 PM
To use MySQL stored procedures in PHP: Use PDO or the MySQLi extension to connect to a MySQL database. Prepare the statement to call the stored procedure. Execute the stored procedure. Process the result set (if the stored procedure returns results). Close the database connection.
How to fix mysql_native_password not loaded errors on MySQL 8.4
Dec 09, 2024 am 11:42 AM
One of the major changes introduced in MySQL 8.4 (the latest LTS release as of 2024) is that the "MySQL Native Password" plugin is no longer enabled by default. Further, MySQL 9.0 removes this plugin completely. This change affects PHP and other app
The difference between oracle database and mysql
May 10, 2024 am 01:54 AM
Oracle database and MySQL are both databases based on the relational model, but Oracle is superior in terms of compatibility, scalability, data types and security; while MySQL focuses on speed and flexibility and is more suitable for small to medium-sized data sets. . ① Oracle provides a wide range of data types, ② provides advanced security features, ③ is suitable for enterprise-level applications; ① MySQL supports NoSQL data types, ② has fewer security measures, and ③ is suitable for small to medium-sized applications.
