The MySQL ADD COLUMN
statement is used to add a new column to an existing table. This statement is essential for modifying the structure of a table to accommodate new data requirements.
ALTER TABLE table_name
ADD COLUMN column_name datatype [constraints];
The ADD COLUMN
statement has the following components:
table_name
: The name of the table to be altered.column_name
: The name of the new column to be added.datatype
: The data type of the new column (e.g., INT
, VARCHAR(100)
, DATE
).[constraints]
: Optional constraints for the new column (e.g., PRIMARY KEY
, NOT NULL
, UNIQUE
).Let's look at an example of the MySQL ADD COLUMN
statement and how to use it:
USE mydatabase;
This query sets the context to the database named mydatabase
.
Create a table to work with:
CREATE TABLE employees (
id INT AUTO_INCREMENT PRIMARY KEY,
first_name VARCHAR(50) NOT NULL,
last_name VARCHAR(50) NOT NULL,
email VARCHAR(100) UNIQUE
);
This query creates a table named employees
with columns for id
, first_name
, last_name
, and email
.
Add a new column to the table:
ALTER TABLE employees
ADD COLUMN date_of_birth DATE;
This query adds a new column named date_of_birth
to the employees
table.
To verify that the column has been added, you can describe the table structure:
DESCRIBE employees;
This query provides a detailed description of the employees
table structure, including the new column.
The MySQL ADD COLUMN
statement is a powerful tool for modifying the structure of existing tables to accommodate new data requirements. Understanding how to use the ADD COLUMN
statement is essential for effective database management in MySQL.