Methods to add fields in the table: 1. Use the "ALTER TABLE table name ADD new field name data type;" statement to add fields at the end; 2. Use "ALTER TABLE table name ADD new field name data type FIRST ;" statement adds fields at the beginning; 3. Use the "ALTER TABLE table name ADD new field name data type [constraints] AFTER existing field name;" statement to add fields in the middle.
The operating environment of this tutorial: windows7 system, mysql8 version, Dell G3 computer.
How to add fields in the table in Mysql database
1. 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><數(shù)據(jù)類型>[約束條件];
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.
2. Add a field 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> <數(shù)據(jù)類型> [約束條件] FIRST;
The FIRST keyword is generally placed at the end of the statement.
3. Add fields in the middle position
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 position (after the specified field ) to add a field, you need to use the AFTER keyword at this time, the syntax format is as follows:
ALTER TABLE <表名> ADD <新字段名> <數(shù)據(jù)類型> [約束條件] AFTER <已經(jīng)存在的字段名>;
The 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:
Use DESC to view the student table structure
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)
1. Add an INT type at the end The field age
mysql> ALTER TABLE student ADD age INT(4); Query OK, 0 rows affected (0.16 sec) Records: 0 Duplicates: 0 Warnings: 0 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)
2. Add the INT type field stuId
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)
#3 in the first column of the table. After the name field Add a field named stuno with data type INT
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)
(Recommended tutorial: mysql video tutorial)
The above is the detailed content of How to add fields to the database table. 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
Undress AI Tool
Undress images for free
Undresser.AI Undress
AI-powered app for creating realistic nude photos
AI Clothes Remover
Online AI tool for removing clothes from photos.
Clothoff.io
AI clothes remover
Video Face Swap
Swap faces in any video effortlessly with our completely free AI face swap tool!
Hot Article
Guide: Stellar Blade Save File Location/Save File Lost/Not Saving4 weeks ago By DDDAgnes Tachyon Build Guide | A Pretty Derby Musume2 weeks ago By Jack chenOguri Cap Build Guide | A Pretty Derby Musume2 weeks ago By Jack chenDune: Awakening - Advanced Planetologist Quest Walkthrough4 weeks ago By Jack chenDate Everything: Dirk And Harper Relationship Guide4 weeks ago By Jack chen
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
Performing logical backups using mysqldump in MySQL
Jul 06, 2025 am 02:55 AM
mysqldump is a common tool for performing logical backups of MySQL databases. It generates SQL files containing CREATE and INSERT statements to rebuild the database. 1. It does not back up the original file, but converts the database structure and content into portable SQL commands; 2. It is suitable for small databases or selective recovery, and is not suitable for fast recovery of TB-level data; 3. Common options include --single-transaction, --databases, --all-databases, --routines, etc.; 4. Use mysql command to import during recovery, and can turn off foreign key checks to improve speed; 5. It is recommended to test backup regularly, use compression, and automatic adjustment.
Handling NULL Values in MySQL Columns and Queries
Jul 05, 2025 am 02:46 AM
When handling NULL values ??in MySQL, please note: 1. When designing the table, the key fields are set to NOTNULL, and optional fields are allowed NULL; 2. ISNULL or ISNOTNULL must be used with = or !=; 3. IFNULL or COALESCE functions can be used to replace the display default values; 4. Be cautious when using NULL values ??directly when inserting or updating, and pay attention to the data source and ORM framework processing methods. NULL represents an unknown value and does not equal any value, including itself. Therefore, be careful when querying, counting, and connecting tables to avoid missing data or logical errors. Rational use of functions and constraints can effectively reduce interference caused by NULL.
Aggregating data with GROUP BY and HAVING clauses in MySQL
Jul 05, 2025 am 02:42 AM
GROUPBY is used to group data by field and perform aggregation operations, and HAVING is used to filter the results after grouping. For example, using GROUPBYcustomer_id can calculate the total consumption amount of each customer; using HAVING can filter out customers with a total consumption of more than 1,000. The non-aggregated fields after SELECT must appear in GROUPBY, and HAVING can be conditionally filtered using an alias or original expressions. Common techniques include counting the number of each group, grouping multiple fields, and filtering with multiple conditions.
Paginating Results with LIMIT and OFFSET in MySQL
Jul 05, 2025 am 02:41 AM
MySQL paging is commonly implemented using LIMIT and OFFSET, but its performance is poor under large data volume. 1. LIMIT controls the number of each page, OFFSET controls the starting position, and the syntax is LIMITNOFFSETM; 2. Performance problems are caused by excessive records and discarding OFFSET scans, resulting in low efficiency; 3. Optimization suggestions include using cursor paging, index acceleration, and lazy loading; 4. Cursor paging locates the starting point of the next page through the unique value of the last record of the previous page, avoiding OFFSET, which is suitable for "next page" operation, and is not suitable for random jumps.
Implementing Transactions and Understanding ACID Properties in MySQL
Jul 08, 2025 am 02:50 AM
MySQL supports transaction processing, and uses the InnoDB storage engine to ensure data consistency and integrity. 1. Transactions are a set of SQL operations, either all succeed or all fail to roll back; 2. ACID attributes include atomicity, consistency, isolation and persistence; 3. The statements that manually control transactions are STARTTRANSACTION, COMMIT and ROLLBACK; 4. The four isolation levels include read not committed, read submitted, repeatable read and serialization; 5. Use transactions correctly to avoid long-term operation, turn off automatic commits, and reasonably handle locks and exceptions. Through these mechanisms, MySQL can achieve high reliability and concurrent control.
Calculating Database and Table Sizes in MySQL
Jul 06, 2025 am 02:41 AM
To view the size of the MySQL database and table, you can query the information_schema directly or use the command line tool. 1. Check the entire database size: Execute the SQL statement SELECTtable_schemaAS'Database',SUM(data_length index_length)/1024/1024AS'Size(MB)'FROMinformation_schema.tablesGROUPBYtable_schema; you can get the total size of all databases, or add WHERE conditions to limit the specific database; 2. Check the single table size: use SELECTta
Handling character sets and collations issues in MySQL
Jul 08, 2025 am 02:51 AM
Character set and sorting rules issues are common when cross-platform migration or multi-person development, resulting in garbled code or inconsistent query. There are three core solutions: First, check and unify the character set of database, table, and fields to utf8mb4, view through SHOWCREATEDATABASE/TABLE, and modify it with ALTER statement; second, specify the utf8mb4 character set when the client connects, and set it in connection parameters or execute SETNAMES; third, select the sorting rules reasonably, and recommend using utf8mb4_unicode_ci to ensure the accuracy of comparison and sorting, and specify or modify it through ALTER when building the library and table.
Setting up asynchronous primary-replica replication in MySQL
Jul 06, 2025 am 02:52 AM
To set up asynchronous master-slave replication for MySQL, follow these steps: 1. Prepare the master server, enable binary logs and set a unique server-id, create a replication user and record the current log location; 2. Use mysqldump to back up the master library data and import it to the slave server; 3. Configure the server-id and relay-log of the slave server, use the CHANGEMASTER command to connect to the master library and start the replication thread; 4. Check for common problems, such as network, permissions, data consistency and self-increase conflicts, and monitor replication delays. Follow the steps above to ensure that the configuration is completed correctly.
