add unique email and username constraint

db/init.sql

@@ -20,8 +20,8 @@ CREATE TABLE IF NOT EXISTS tickets (
 CREATE TABLE IF NOT EXISTS users (
   user_ID INT AUTO_INCREMENT PRIMARY KEY,
   user_name CHAR(255),
-  username CHAR(255),
-  user_email VARCHAR(255),
+  username CHAR(255) UNIQUE,
+  user_email VARCHAR(255) UNIQUE,
   user_hashedPass CHAR(255),
   isAdmin BOOLEAN
 );