Will MySQL work if we won’t include the size of VARCHAR while creating a new table?

No, the query won’t work. Let’s create the same scenario and check the error −

mysql> create table DemoTable1821
     (
     Id int,
     FirstName varchar,
     LastName varchar
     );
ERROR 1064 (42000): You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near ',
LastName varchar
)' at line 4

To remove the above error, you need to give the size of varchar(10). Let us first create a table −

mysql> create table DemoTable1821
     (
     Id int,
     FirstName varchar(10),
     LastName varchar(10)
     );
Query OK, 0 rows affected (0.00 sec)

Insert some records in the table using insert command −

mysql> insert into DemoTable1821 values(1,'John','Smith');
Query OK, 1 row affected (0.00 sec)
mysql> insert into DemoTable1821 values(2,'John','Doe');
Query OK, 1 row affected (0.00 sec)
mysql> insert into DemoTable1821 values(3,'Adam','Smith');
Query OK, 1 row affected (0.00 sec)

Display all records from the table using select statement −

mysql> select * from DemoTable1821;

This will produce the following output −

+------+-----------+----------+
| Id   | FirstName | LastName |
+------+-----------+----------+
|    1 | John      |    Smith |
|    2 | John      |       Doe|
|    3 | Adam      |    Smith |
+------+-----------+----------+
3 rows in set (0.00 sec)