Does using SERIAL as column name already includes 'NOT NULL' in MySQL?

In MySQL, SERIAL is an alias for BIGINT UNSIGNED NOT NULL AUTO_INCREMENT UNIQUE. So, do not use NOT NULL after SERIAL, since it already includes NOT NULL as part of its definition.

Let us see an example and create a table. Here, we have a column with the name “serial” −

mysql> create table DemoTable
(
   Id serial
);
Query OK, 0 rows affected (0.42 sec)

Insert some records in the table using insert command. We aren’t including any value while inserting −

mysql> insert into DemoTable values();
Query OK, 1 row affected (0.24 sec)
mysql> insert into DemoTable values();
Query OK, 1 row affected (0.09 sec)
mysql> insert into DemoTable values();
Query OK, 1 row affected (0.06 sec)
mysql> insert into DemoTable values();
Query OK, 1 row affected (0.14 sec)
mysql> insert into DemoTable values();
Query OK, 1 row affected (0.09 sec)
mysql> insert into DemoTable values();
Query OK, 1 row affected (0.07 sec)

Display all records from the table using select statement −

mysql> select *from DemoTable;

This will produce the following output −

+----+
| Id |
+----+
|  1 |
|  2 |
|  3 |
|  4 |
|  5 |
|  6 |
+----+
6 rows in set (0.00 sec)