How to modify a MySQL column to allow NULL?

For our example, let's create a table with a NOT NULL constraint. After that, we'll modify a column to allow NULL.

The following is the query to create a table with NOT NULL constraints.

mysql> create table AllowNullDemo
   -> (
   -> id int not null
   -> );
Query OK, 0 rows affected (0.48 sec)=

Use the INSERT command to insert records. The query is as follows.

mysql> insert into AllowNullDemo values();
Query OK, 1 row affected, 1 warning (0.19 sec)

mysql> insert into AllowNullDemo values();
Query OK, 1 row affected, 1 warning (0.15 sec)

Display recorded query.

mysql> select *from AllowNullDemo;

This is the output result. Since we did not add any value when using the INSERT command above, the value 0 is displayed.

+----+
| id |
+----+
|  0 |
|  0 |
+----+
2 rows in set (0.00 sec)

This is the syntax that allows NULL values.

alter table yourTableName  modify column yourColumnName datatype;

Apply the above syntax to modify the column to allow NULL. The query is as follows.

mysql> alter table AllowNullDemo modify column id int;
Query OK, 0 rows affected (1.59 sec)
Records: 0  Duplicates: 0  Warnings: 0

After executing the above query, you can insert a NULL value into the column because the column has been successfully modified in the above operation.

mysql>  insert into AllowNullDemo values();
Query OK, 1 row affected (0.15 sec)

Display records to check if the last inserted value is NULL.

mysql> select *from AllowNullDemo;

The following is the output, where NULL values ​​are now visible.

+------+
| id   |
+------+
|    0 |
|    0 |
| NULL |
+------+
3 rows in set (0.00 sec)

Using the above method, we can easily modify the MySQL column to allow NULL.

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