AUTO_INCREMENT in MySQL can be signed by default?

Yes, the AUTO_INCREMENT in MySQL will be signed (Positive and Negative Value both) by default.

Let us first create a table −

mysql> create table DemoTable
   -> (
   -> MyNumber int AUTO_INCREMENT PRIMARY KEY
   -> );
Query OK, 0 rows affected (0.45 sec)

Insert some records in the table using insert command. Here, we have set negative values as well for AUTO_INCREMENT column −

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

mysql> insert into DemoTable values(-100);
Query OK, 1 row affected (0.12 sec)

mysql> insert into DemoTable values(-300);
Query OK, 1 row affected (0.13 sec)

mysql> insert into DemoTable values(0);
Query OK, 1 row affected (0.18 sec)

Display all records from the table using select statement −

mysql> select *from DemoTable;

Output

+----------+
| MyNumber |
+----------+
|   -300   |
|   -100   |
|      1   |
|      2   |
+----------+
4 rows in set (0.00 sec)