Adding a new NOT NULL column to an existing table with records

To add a new NOT NULL column to an already created table, use ALTER command. Let us first create a table −

mysql> create table DemoTable
   -> (
   -> StudentId int NOT NULL AUTO_INCREMENT PRIMARY KEY,
   -> StudentName varchar(20)
   -> );
Query OK, 0 rows affected (0.60 sec)

Following is the query to add a new NOT NULL column to an existing table −

mysql> alter table DemoTable add column StudentAge int NOT NULL;
Query OK, 0 rows affected (0.52 sec)
Records: 0 Duplicates: 0 Warnings: 0

Insert some records in the table using insert command −

mysql> insert into DemoTable(StudentName,StudentAge) values('Chris',21);
Query OK, 1 row affected (0.14 sec)
mysql> insert into DemoTable(StudentName,StudentAge) values('David',23);
Query OK, 1 row affected (0.13 sec)
mysql> insert into DemoTable(StudentName,StudentAge) values('Mike',NULL);
ERROR 1048 (23000): Column 'StudentAge' cannot be null

Display all records from the table using select statement −

mysql> select * from DemoTable;

This will produce the following output −

+-----------+-------------+------------+
| StudentId | StudentName | StudentAge |
+-----------+-------------+------------+
|         1 | Chris       |         21 |
|         2 | David       |         23 |
+-----------+-------------+------------+
2 rows in set (0.00 sec)