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How to add NOT NULL constraint to an already created MySQL column?
Achieve this using ALTER TABLE. Let us first create a table −
mysql> create table DemoTable -> ( -> StudentId int NOT NULL AUTO_INCREMENT PRIMARY KEY, -> StudentName varchar(100) -> ); Query OK, 0 rows affected (0.86 sec)
Let us check the description of the table −
mysql> desc DemoTable;
This will produce the following output −
+-------------+--------------+------+-----+---------+----------------+ | Field | Type | Null | Key | Default | Extra | +-------------+--------------+------+-----+---------+----------------+ | StudentId | int(11) | NO | PRI | NULL | auto_increment | | StudentName | varchar(100) | YES | | NULL | | +-------------+--------------+------+-----+---------+----------------+ 2 rows in set (0.01 sec)
Here is the query to add a NOT NULL constraint to the other column “StudentName”, which wasn’t set NOT NULL initially −
mysql> alter table DemoTable modify StudentName varchar(100) NOT NULL; Query OK, 0 rows affected (1.57 sec) Records: 0 Duplicates: 0 Warnings: 0
Let us check the description of the table once again −
mysql> desc DemoTable;
This will produce the following output −
+-------------+--------------+------+-----+---------+----------------+ | Field | Type | Null | Key | Default | Extra | +-------------+--------------+------+-----+---------+----------------+ | StudentId | int(11) | NO | PRI | NULL | auto_increment | | StudentName | varchar(100) | NO | | NULL | | +-------------+--------------+------+-----+---------+----------------+ 2 rows in set (0.00 sec)
Updated on: 30-Jul-2019
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