How to add a new column to an existing table

The ALTER TABLE command with the ADD operator is used to add a new column to an existing table.

Syntax

MySQL 8.1
ALTER TABLE table_name
ADD column_name data_type [constraints];

Example

Suppose we have a table employees, and we want to add a column email of type VARCHAR(255).

MySQL 8.1
ALTER TABLE employees
ADD email VARCHAR(255);

Adding a column with a NOT NULL constraint and a default value:

MySQL 8.1
ALTER TABLE employees
ADD date_of_birth DATE NOT NULL DEFAULT '1900-01-01';

Note
When adding a column with a NOT NULL constraint, if there are already existing rows in the table, you must specify a default value; otherwise, an error will occur.