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:

ALTER TABLE table_name CHANGE old_column_name new_column_name new_data_type [column_constraints]

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:

   ALTER TABLE my_table CHANGE age age INT

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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:

   ALTER TABLE my_table CHANGE age age_years INT

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

   ALTER TABLE my_table CHANGE age age INT NOT NULL

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• 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.

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