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Databases Reporting with SQL Aggregate and Numeric Functions Practice Session

Jan Lundeen
Jan Lundeen
5,881 Points

On SQL Playground, Stage 3, Practice, how do I calculate the average movie rating and round it to 1 decimal place?

Hi,

In the Reporting in SQL class, I'm running into some issues with a question in the SQL Playground, Stage 3, Practice section. Here's the question:

Calculate the average rating for each movie and round it to one decimal place.

Here's my query:

SELECT AVG(rating) AS "average_rating", ROUND("average_rating", 1) FROM reviews;

Here's the results:

average_ rating = 3.8 ROUND(β€œaverage_rating”, 1) = 0

I think the average_rating is correct, but the rounded result is not. How do I calculate the average movie rating and round it to 1 decimal place?

Thanks,

Jan

3 Answers

Steven Parker
Steven Parker
229,788 Points

Did you want only one column?

In that case you'd want to enclose the average calculation inside the rounding function instead of listing them as two columns. So it might look like this:

SELECT ROUND(AVG(rating), 1) AS average_rating FROM reviews;

Although it will be a bit hard to confirm with that data set since you apparently get the same result even without rounding.

Jan Lundeen
Jan Lundeen
5,881 Points

Hi Steven,

I tried to put it in one column, but I got a syntax error. When I tried to combine the columns, I used AVG first and ROUND second [e.g. SELECT AVG(ROUND(rating, 1)) AS "average_rating" FROM reviews;]. It looks like I mixed up the order of the commands (should be ROUND, AVG instead of AVG, ROUND) and probably didn't get the parentheses placed correctly.

Originally, when I wrote this question, I listed "average_rating" = 3.8 on one line and ROUND(β€œaverage_rating”, 1) = 0 on the second line. It looks like the results were listed on one line instead. I agree. It will be hard to confirm with that data set.

Thanks for your help!

Jan

Steven Parker
Steven Parker
229,788 Points

Well, you could round the average to 0 places and it should return 4.

Remember when nesting functions, the innermost is performed first, and the outermost is performed last. Just the opposite of peeling an onion.

Hi, the task is asking to calculate EACH rating for EACH movie and round it to one decimal place. To get them all to display don't forget to use a GROUP BY!!

:)

SELECT movie_id,ROUND(AVG(rating),1) AS movie_rating FROM reviews GROUP BY movie_id;

Jan Lundeen
Jan Lundeen
5,881 Points

You're right. That would work. Thanks!

Jan