How to find average of specific records - sql

Question

I'm a little stuck on some work here for my final high school assessment.
The task is essentially to make a database handling movie information.
Tables:
Movie Table, Movie review table
My task is to display the movies along with their reviews then calculate and display an average overall rating.
Visually it should look like this:
Example:
"Movie Title", "Movie Review Rating", "Average Rating"
Titanic , 9 , 8.6
Titanic , 8 , 8.6
Titanic , 9 , 8.6
Star Wars , 4 , 5
Star Wars , 5 , 5
Star Wars , 6 , 5
Matrix , 6 , 8.3
Matrix , 10 , 8.3
Matrix , 9 , 8.3
How would I go about calculating the average for each individual movie?
SELECT
`Movie name`,
`Overall Rating`
AVG(`Average Rating`)
FROM
Movie
INNER JOIN `Movie review`
ON Movie.`Movie Ref` = `Movie review`.`Movie Ref`;

Answer 1

One option uses domain aggregate function:
SELECT MovieRatings.MovieTitle, MovieRatings.MovieReviewRating,
Round(DAvg("MovieReviewRating","MovieRatings","MovieTitle='" &
[MovieTitle] & "'"),1) AS AverageRating FROM MovieRatings;
Or build an aggregate query (open Access query builder and click Totals button on ribbon):
SELECT MovieRatings.MovieTitle, Avg(MovieRatings.MovieReviewRating) AS
AvgOfMovieReviewRating FROM MovieRatings GROUP BY
MovieRatings.MovieTitle;
Then join that query to the table:
SELECT MovieRatings.MovieTitle, MovieRatings.MovieReviewRating,
Round([AvgOfMovieReviewRating],1) AS AverageRating FROM Query1 INNER
JOIN MovieRatings ON Query1.MovieTitle = MovieRatings.MovieTitle;
Here are the 2 queries as all-in-one nested:
SELECT MovieRatings.MovieTitle, MovieRatings.MovieReviewRating,
Round([AvgOfMovieReviewRating],1) AS AverageRating FROM (SELECT
MovieRatings.MovieTitle, Avg(MovieRatings.MovieReviewRating) AS
AvgOfMovieReviewRating FROM MovieRatings GROUP BY
MovieRatings.MovieTitle) AS Query1 INNER JOIN MovieRatings ON
Query1.MovieTitle = MovieRatings.MovieTitle;
The nested query created by first building and saving the aggregate query. Then build second query that references Query1, switch to SQLView and copy/paste the SQL statement of Query1 into second query and save. Can now delete Query1 object.
Grouping and Joining on MovieTitle field but really should be using numeric primary and foreign keys.
Be aware Round() function uses even/odd rule: 9.45 rounds to 9.4 and 9.35 rounds to 9.4.
Advise not to use spaces in naming convention.

Answer 2

You may have misinterpreted the question or are guessing at the data structure. You wouldn't know the averages in advance. If your professor gave you the data with pre-aggregated averages then they didn't teach you correctly because that is not how data is put into a database. i.e. how would you know what to put into the average column if you put the first value in and there are 50,000 values to insert? You would have to wait until all 50,000 values get inserted- then take the average. Then update 50,000 rows of data with this average.
The Movie Review table most likely is a table with two columns- "Movie Title" and "Movie Review Rating". Where each row in the table represents a review. Taking an average would come later after inserting rows into the table with the movie review data.
After data is inserted, an average would be taken similar to:
SELECT MovieTitle, AVG(MovieReviewRating) AS AverageRating
FROM MovieReview
GROUP BY MovieTitle
After confirming the averages, you can join with "Movie Table" for it's columns.