Database Schema and Sql for a 5 star Rating

Question

Requirements:

1. All "Users" have 5 fixed set of same "Services" which they are supposed to rate.
2. Given the userId, display all the Services and their corresponding "Ratings". 
3. Rating would be from a scale of 1 - 5 only
4. Ratings can be updated anytime by the user for any of his Service.

I am no SQL/DB expert and I had this question up in stacks for which I got answer from Raj here ER Model of User Ratings

This is the ER I finalized (open for correction).

My Fetch Query: Get all the services and their corresponding for a userId (say userId = 1)

SELECT service.service_id, service.name, usr.ratings 
FROM services service, 
     ratings ratings, 
     userservices_ratings usr,
     user user,
     user_services us
where 
    us.userid = user.uid and 
    us.serviceid = service.serviceid and
    usr.usid = us.id and
    usr.rid = ratings.rid and
    user.id = 1

1. The above query will return all the services and ratings, only if User has rated the service. For services which are unrated don't make it to result set. So I assume I should pre-populate unrated services with a default value say 0?

2. All users will have fixed set of 5 services all the time, do I write a trigger to create his entry into User_Services table whenever a User is created?

3. How would the create/update query look if for example a Userid = 1, rates = 3 for serviceId = 1?

4. Any flaw in the schema?

Answer 1

You can standard format of Rating Schema here https://schema.org/Rating You can pick required columns from this