Fixes column nullability in MySQL scripts

Some columns of the MySQL database created by the scripts in the "db"
directory where incorrectly set as nullable. This commit fixes this
error and sets them as non nullable columns.

db/mysql-with-inserts.sql

@@ -2,14 +2,14 @@ CREATE DATABASE `daaexample`;
 
 CREATE TABLE `daaexample`.`people` (
 	`id` int NOT NULL AUTO_INCREMENT,
-	`name` varchar(50) DEFAULT NULL,
-	`surname` varchar(100) DEFAULT NULL,
+	`name` varchar(50) NOT NULL,
+	`surname` varchar(100) NOT NULL,
 	PRIMARY KEY (`id`)
 );
 
 CREATE TABLE `daaexample`.`users` (
 	`login` varchar(100) NOT NULL,
-	`password` varchar(64) DEFAULT NULL,
+	`password` varchar(64) NOT NULL,
 	PRIMARY KEY (`login`)
 );
 

db/mysql.sql

@@ -2,15 +2,15 @@ CREATE DATABASE `daaexample`;
 
 CREATE TABLE `daaexample`.`people` (
 	`id` int NOT NULL AUTO_INCREMENT,
-	`name` varchar(50) DEFAULT NULL,
-	`surname` varchar(100) DEFAULT NULL,
+	`name` varchar(50) NOT NULL,
+	`surname` varchar(100) NOT NULL,
 	PRIMARY KEY (`id`)
 );
 
 CREATE TABLE `daaexample`.`users` (
 	`login` varchar(100) NOT NULL,
-	`password` varchar(64) DEFAULT NULL,
+	`password` varchar(64) NOT NULL,
 	PRIMARY KEY (`login`)
 );
 
-GRANT ALL ON `daaexample`.* TO 'daa'@'localhost' IDENTIFIED BY 'daa';
\ No newline at end of file
+GRANT ALL ON `daaexample`.* TO 'daa'@'localhost' IDENTIFIED BY 'daa';