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Set NOT NULL attribute to an existing column in MySQL
To set NOT NULL attribute to an existing column, use ALTER TABLE command. Let us first create a table −
mysql> create table DemoTable1949 ( UserId int, UserName varchar(20) ); Query OK, 0 rows affected (0.00 sec)
Here is the query to set NOT NULL attribute to an existing column −
mysql> alter table DemoTable1949 modify UserName varchar(20) not null; Query OK, 0 rows affected (0.00 sec) Records: 0 Duplicates: 0 Warnings: 0
Let us check the description of table −
mysql> desc DemoTable1949;
This will produce the following output −
+----------+-------------+------+-----+---------+-------+ | Field | Type | Null | Key | Default | Extra | +----------+-------------+------+-----+---------+-------+ | UserId | int(11) | YES | | NULL | | | UserName | varchar(20) | NO | | NULL | | +----------+-------------+------+-----+---------+-------+ 2 rows in set (0.00 sec)
Insert some records in the table using insert command −
mysql> insert into DemoTable1949 values(101,NULL); ERROR 1048 (23000): Column 'UserName' cannot be null mysql> insert into DemoTable1949 values(101,'Chris'); Query OK, 1 row affected (0.00 sec) mysql> insert into DemoTable1949 values(102,'Bob'); Query OK, 1 row affected (0.00 sec)
Display all records from the table using select statement −
mysql> select * from DemoTable1949;
This will produce the following output −
+--------+----------+ | UserId | UserName | +--------+----------+ | 101 | Chris | | 102 | Bob | +--------+----------+ 2 rows in set (0.00 sec)
Updated on: 31-Dec-2019
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