In MySQL, the DEFAULT constraint is used to insert value into a column in a table. If there is no value is specified for a column then the default value will be added to column for all new records.

DEFAULT Constraint on CREATE TABLE

The following statement creates a DEFAULT constraint on the "country" column when the "employee" table is created.

Example:

CREATE TABLE employee
(
id int NOT NULL,
first_name varchar(45) NOT NULL,
last_name varchar(45),
country varchar(45) DEFAULT 'Canada'
);

DEFAULT Constraint on ALTER TABLE

We can also create DEFAULT constraint on a column when the table is already created, for that we use ALTER command. The below statement creates a DEFAULT constraint on the "country" column when the table "employee" is already created:

ALTER TABLE employee
ALTER country SET DEFAULT 'Canada';

To DROP a DEFAULT Constraint

We can also drop a DEFAULT constraint. To drop a DEFAULT constraint, use the below statement:

ALTER TABLE employee
ALTER country DROP DEFAULT;

Hope this will help you :)