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Change a MySQL column to have NOT NULL constraint
To update the constraint, use the MODIFY command. Following is the syntax −
alter table yourTableName modify yourExistingColumnName yourExistingDataType NOT NULL;
Let us first create a table −
mysql> create table DemoTable -> ( -> UserId int NOT NULL AUTO_INCREMENT, -> UserFirstName varchar(100), -> UserLastName varchar(100), -> UserEmailId varchar(100), -> UserPassword varchar(100), -> PRIMARY KEY(UserId) -> ); Query OK, 0 rows affected (0.91 sec)
Following is the query to change the constraint of a column to NOT NULL −
mysql> alter table DemoTable modify UserFirstName varchar(100) NOT NULL; Query OK, 0 rows affected (2.13 sec) Records: 0 Duplicates: 0 Warnings: 0
Let us use the desc command to check whether the column has NOT NULL constraint or not −
mysql> desc DemoTable;
Output
This will produce the following output. Now the UserFirstName column has NOT NULL constraint −
+---------------+--------------+------+-----+---------+----------------+ | Field | Type | Null | Key | Default | Extra | +---------------+--------------+------+-----+---------+----------------+ | UserId | int(11) | NO | PRI | NULL | auto_increment | | UserFirstName | varchar(100) | NO | | NULL | | | UserLastName | varchar(100) | YES | | NULL | | | UserEmailId | varchar(100) | YES | | NULL | | | UserPassword | varchar(100) | YES | | NULL | | +---------------+--------------+------+-----+---------+----------------+ 5 rows in set (0.17 sec)
Updated on: 30-Jun-2020
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