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Development Tools Database Foundations SQL Calculating, Aggregating and Other Functions Grouping, Joining and Cleaning Up

Posted by Julius Dockwarder
Julius Dockwarder
15,041 Points

Database Foundations Challenge

I'm dying!

Darren Joy
Darren Joy
19,573 Points
Darren Joy
Darren Joy
19,573 Points

I hear yah brutha!

I need to go through that stuff again too. I got about 2/3rds of the way through and had to take a break...

It's not so much hard, as tedious. I just can;t remember all the little nuances of calling this and wildcarding that.

4 Answers

Lucy Cockerill
Lucy Cockerill
8,798 Points

Don't know if you managed to figure this one out... but correct answer is:

SELECT title, IFNULL(AVG(score),0) AS average FROM reviews RIGHT OUTER JOIN movies ON movies.id = reviews.movie_id GROUP BY movie_id HAVING average < 2;
Carsten Dollerup
Carsten Dollerup
9,278 Points
Carsten Dollerup
Carsten Dollerup
9,278 Points

Thanks, Lucy. My mistake was different, but your reply helped me out to by going through your reply.

Julius Dockwarder
Julius Dockwarder
15,041 Points
Julius Dockwarder
Julius Dockwarder
15,041 Points

Like before, select the average "score" as "average", setting to 0 if null, by grouping the "movie_id" from the "reviews" table. Also, do an outer join on the "movies" table with its "id" column and display the movie "title" before the "average". Finally, include averages under 2.

SELECT IFNULL(AVG(score), 0) AS average FROM reviews LEFT OUTER JOIN movies ON movies.id = reviews.title GROUP BY movie_id HAVING average < 2;

What's wrong with it? :'(

Carsten Dollerup
Carsten Dollerup
9,278 Points
Carsten Dollerup
Carsten Dollerup
9,278 Points

I hope this helps someone, as I was a bit confused about this one too.

Julius' problem was trying to get the title from the reviews table. My mistake was trying to join the tables with: "...FROM reviews LEFT OUTER JOIN movies"... which obviously then does not generate the movie which has no scores. That's why the "RIGHT OUTER JOIN movies..." is correct to use.

Best Regards and keep it up all! :-)

Amed Alberto Sanchez
seal-mask
.a{fill-rule:evenodd;}techdegree
Amed Alberto Sanchez
Python Development Techdegree Student 2,879 Points
Amed Alberto Sanchez
.a{fill-rule:evenodd;}techdegree
Amed Alberto Sanchez
Python Development Techdegree Student 2,879 Points

The correct answer is: 

SELECT movies.title, IFNULL(AVG(reviews.score),0) AS average
FROM reviews
RIGHT OUTER JOIN movies ON movies.id = reviews.movie_id
GROUP BY reviews.movie_id
HAVING average <= 2

Courtesy of Eric Butler. Check the other discussion on this topic https://teamtreehouse.com/community/code-challenge-3-2