How to add, modify and delete MySQL data table field operation guide

Field operation guide in MySQL: Add, modify, and delete fields. Add field: ALTER TABLE table_name ADD column_name data_type [NOT NULL] [DEFAULT default_value] [PRIMARY KEY] [AUTO_INCREMENT] Modify field: ALTER TABLE table_name MODIFY column_name data_type [NOT NULL] [DEFAULT default_value] [PRIMARY KEY]

MySQL Data Table Field Operation Guide: Add, Modify and Delete

In a MySQL database, fields are the basic units for storing data in a table. Adding, modifying, and deleting fields are common data table management tasks. This article will explain in detail how to perform these operations.

Add fields

grammar:

 <code class="sql">ALTER TABLE table_name ADD column_name data_type [NOT NULL] [DEFAULT default_value] [PRIMARY KEY] [AUTO_INCREMENT]</code>

Example:

 <code class="sql">ALTER TABLE users ADD email VARCHAR(255) NOT NULL</code>

This adds a VARCHAR(255) field named email to the users table and sets it to non-empty.

Modify fields

grammar:

 <code class="sql">ALTER TABLE table_name MODIFY column_name data_type [NOT NULL] [DEFAULT default_value] [PRIMARY KEY] [AUTO_INCREMENT]</code>

Example:

 <code class="sql">ALTER TABLE users MODIFY name VARCHAR(100)</code>

This will change the data type of the name field in the users table to VARCHAR(100).

Delete fields

grammar:

 <code class="sql">ALTER TABLE table_name DROP COLUMN column_name</code>

Example:

 <code class="sql">ALTER TABLE users DROP COLUMN email</code>

This will delete the email field from the users table.

Notes:

• Before performing field operations, make sure you have sufficient permissions.
• Field modifications may affect existing data. Please make careful modifications.
• Deleting a field will delete all data in that field forever.
• When adding or modifying the primary key field, you need to re-index.
• The auto-increment field can only be set when adding fields.

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