How to use change in mysql

The CHANGE keyword in MySQL is used to modify the data type or attributes of existing columns in the table. Syntax: ALTER TABLE table_name CHANGE old_column_name new_column_name new_data_type [column_constraints]. It can modify data types, column names, or add constraints, but it will not affect data integrity. Modifying column names requires updating references, and it cannot modify primary keys or auto-increment columns.

Usage of CHANGE in MySQL

Question: What is the usage of CHANGE in MySQL?

Answer:
The CHANGE keyword is used to modify the data type or attributes of an existing column in a MySQL table.

Syntax:

<code>ALTER TABLE table_name
CHANGE old_column_name new_column_name new_data_type [column_constraints]</code>

Parameters:

• table_name: The table to be modified The name of
• old_column_name: The name of the existing column to modify
• new_column_name: Optional, the name of the modified column (if not If specified, it will remain as is)
• new_data_type: The new data type to be modified
• column_constraints: Optional, constraints of the new column ( For example NOT NULL, UNIQUE, etc.)

Usage:

1. Modify data type:
   Change Change the column's data type from VARCHAR(255) to INT:

   <code>ALTER TABLE my_table CHANGE age age INT</code>

2. Modify the column name and data type:
   Also change the column name from "age" Add constraints for "age_years" and change its data type to INT:

   <code>ALTER TABLE my_table CHANGE age age_years INT</code>

3. Change the column's data type to INT and add NOT NULL constraint:

   <code>ALTER TABLE my_table CHANGE age age INT NOT NULL</code>

   
   

Note:

CHANGE does not affect the integrity of existing data.

• When modifying the data type, ensure that the new type can accommodate the existing data.
• When a column name is modified, any references to the column (such as foreign keys) will become invalid and need to be updated.
• CHANGE cannot be used to modify primary key columns or auto-increment columns.

The above is the detailed content of How to use change in mysql. For more information, please follow other related articles on the PHP Chinese website!