How to modify column default value in MySQL?

Let us first create a table −

mysql> create table DemoTable (    UserId int NOT NULL AUTO_INCREMENT PRIMARY KEY,    UserName varchar(20) DEFAULT 'John' ); Query OK, 0 rows affected (0.76 sec)

Let us check the description of table −

mysql> desc DemoTable;

This will produce the following output −

+----------+-------------+------+-----+---------+----------------+ | Field | Type | Null | Key | Default | Extra | +----------+-------------+------+-----+---------+----------------+ | UserId | int(11) | NO | PRI | NULL | auto_increment | | UserName | varchar(20) | YES | | John | | +----------+-------------+------+-----+---------+----------------+ 2 rows in set (0.00 sec)

Insert some records in the table using insert command −

mysql> insert into DemoTable values(); Query OK, 1 row affected (0.17 sec)

Following is the query to display all records from the table using select statement −

mysql> select *from DemoTable;

This will produce the following output −

+--------+----------+ | UserId | UserName | +--------+----------+ | 1 | John | +--------+----------+ 1 row in set (0.00 sec)

Here is the query to modify column default value. We have set the default UserName to Chris −

mysql> alter table DemoTable modify UserName varchar(20) DEFAULT 'Chris'; Query OK, 0 rows affected (0.19 sec) Records: 0 Duplicates: 0 Warnings: 0

Let us check the description of table using desc command −

mysql> desc DemoTable;

This will produce the following output −

+----------+-------------+------+-----+---------+----------------+ | Field    | Type        | Null | Key | Default | Extra         | +----------+-------------+------+-----+---------+----------------+ | UserId   | int(11)     | NO | PRI | NULL | auto_increment | | UserName | varchar(20) | YES | | Chris | | +----------+-------------+------+-----+---------+----------------+ 2 rows in set (0.00 sec)

Now insert some records in the table using insert command. Since we haven’t added a name, therefore the default “Chris” will get added −

mysql> insert into DemoTable values(); Query OK, 1 row affected (0.11 sec)

Following is the query to display all records from the table using select statement −

mysql> select *from DemoTable;

This will produce the following output −

+--------+----------+ | UserId | UserName | +--------+----------+ | 1      | John   | | 2      | Chris | +--------+----------+ 2 rows in set (0.00 sec)