mysql view users vs admin users syntax inquiry - mysql

Question

Setting up JDBC security realm with Glassfish and I came across this link that provides user control access (admin vs view users). here is the link for this tutorial.
http://jugojava.blogspot.com.eg/2011/02/jdbc-security-realm-with-glassfish-and.html?showComment=1459000091065#c232448315667617784
Few things I didn't understand in the guide and I hope if you can help. What do the lines below mean? (full sql code at the end of of the question)
KEY `fk_users_has_groups_groups1` (`group_id`),
KEY `fk_users_has_groups_users` (`user_id`),
I don't see any table named u but the code is using u.*. The code at the very bottom doesn't have "u" table in it. However, I see the reference to "u" in the inner Join. Can I do select u. based on this INNER JOIN?
CREATE VIEW `v_user_role` AS
SELECT u.username, u.password, g.group_name
FROM `user_groups` ug
INNER JOIN `users` u ON u.user_id = ug.user_id
INNER JOIN `groups` g ON g.group_id = ug.group_id;
Here is the full Code
CREATE TABLE `groups` (
`group_id` int(10) NOT NULL,
`group_name` varchar(20) NOT NULL,
`group_desc` varchar(200) DEFAULT NULL,
PRIMARY KEY (`group_id`)
);
CREATE TABLE `users` (
`user_id` int(10) NOT NULL AUTO_INCREMENT,
`username` varchar(10) NOT NULL,
`first_name` varchar(20) DEFAULT NULL,
`middle_name` varchar(20) DEFAULT NULL,
`last_name` varchar(20) DEFAULT NULL,
`password` char(32) NOT NULL,
PRIMARY KEY (`user_id`)
);
CREATE TABLE `user_groups` (
`user_id` int(10) NOT NULL,
`group_id` int(10) NOT NULL,
PRIMARY KEY (`user_id`,`group_id`),
KEY `fk_users_has_groups_groups1` (`group_id`),
KEY `fk_users_has_groups_users` (`user_id`),
CONSTRAINT `fk_groups` FOREIGN KEY (`group_id`) REFERENCES `groups` (`group_id`) ON DELETE NO ACTION ON UPDATE NO ACTION,
CONSTRAINT `fk_users` FOREIGN KEY (`user_id`) REFERENCES `users` (`user_id`) ON DELETE NO ACTION ON UPDATE NO ACTION
);
CREATE VIEW `v_user_role` AS
SELECT u.username, u.password, g.group_name
FROM `user_groups` ug
INNER JOIN `users` u ON u.user_id = ug.user_id
INNER JOIN `groups` g ON g.group_id = ug.group_id;
INSERT INTO `groups`(`group_id`,`group_name`,`group_desc`) VALUES
(1,'USER','Regular users'),
(2,'ADMIN','Administration users');
INSERT INTO `users`(`user_id`,`username`,`first_name`,`middle_name`,`last_name`,`password`) VALUES
(1,'john','John',NULL,'Doe','6e0b7076126a29d5dfcbd54835387b7b'), /*john123*/
(2,'admin',NULL,NULL,NULL,'21232f297a57a5a743894a0e4a801fc3'); /*admin*/
INSERT INTO `user_groups`(`user_id`,`group_id`) VALUES (1,1),(2,1),(2,2);

Answer 1

1) KEY indicates that those fields are indexed. The index is not unique. See create index documentation.
2) The "u" is an alias, specifically it is a table alias. You can use aliases to refer to a table or field name under a different name. An alias is specific to a query. The alias is defined in the from clause:
`users` u