mysql relational question. Get results when M:N null

-Goal-

I would like to fetch users who do not have an entry within the 'bar' table. These users will also belong to a certain 'usergroup' and have restrictions within the 'user' table itself.

Simplified table structure

User

userid - auto-increment    
username - string    
userage - integer    
usergroup_usergroupid - foreign key

usergroup

usergroup - auto-increment    
usergroupname - string

user_has_bar

user_userid - foreign key    
bar_barid - foreign key

-Query...so far-

SELECT username     
FROM user as u, usergroup as ug, user_has_bar as ub    
WHERE    
u.usergroup_usergroupid = ug.usergroupid AND    
u.userage = 10 AND  <-- lets pretend this exists    
u.location_locationid = 1 AND <-- Same here     
u.userid ... ub.user_userid;

-Headache-

It is this last line that has me throwing up blanks. I believe from what I have read up on, the way to perform this operation is with a LEFT JOIN. However, everything i have read so far ends up b开发者_StackOverflow社区eing quite confusing.

If possible, I would like to keep this operation within a mySQL query and then optimise later.It is created by a PHP mySQL generator I coded and I would like to understand the simple syntax and then dig more in to it. Any approach is VERY welcome though

Thank you kindly for reading this question.

SELECT username
    FROM user u
        INNER JOIN usergroup ug
            ON u.usergroup_usergroupid = ug.usergroupid 
        LEFT JOIN user_has_bar ub
            ON u.userid = ub.user_userid
    WHERE u.userage = 10
        AND u.location_locationid = 1
        AND ub.user_userid IS NULL