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Databases

Posted by Wellington Souza
Wellington Souza
3,121 Points

Your Query Didn't Perform The Correct Count

"In the library database there's a books table. There are id, title, author, genre and first_published columns. Count all the books in each genre. Include the genre column first and the genre_count as the second column of information."

This is what I entered and I do not understand what is wrong.

SELECT genre, COUNT(genre) AS genre_count FROM books GROUP BY genre;

3 Answers

Steven Parker
Steven Parker
229,670 Points
Steven Parker
Steven Parker
229,670 Points

Don't restrict your count.

You're already grouping by genre, so just count the rows ("COUNT(*)" or "COUNT(1)").

Dustin Beaulieu
Dustin Beaulieu
1,279 Points
Dustin Beaulieu
Dustin Beaulieu
1,279 Points

This worked but I do not understand why the result is different. Can you elaborate on this?

Steven Parker
Steven Parker
229,670 Points
Steven Parker
Steven Parker
229,670 Points

The COUNT function only counts rows that have a NOT NULL value in the field(s) you specify as an argument, so the original query didn't return the right count for the null genre.

Dustin Beaulieu
Dustin Beaulieu
1,279 Points
Dustin Beaulieu
Dustin Beaulieu
1,279 Points

I am running into the same issue as above, and my code is identical. I believe the issue is that there is a genre that is null, with a count of 0. I then tried the statement below:

SELECT genre, COUNT(genre) AS "genre_count" FROM books WHERE genre IS NOT NULL GROUP BY genre;

This provided the results I wanted!!! .......but it still says it is not correct. UGH!

Steven Parker
Steven Parker
229,670 Points
Steven Parker
Steven Parker
229,670 Points

I believe the challenge wants to see the null genre included, so you need an unrestricted count and no filter ("WHERE" clause).

Dustin Beaulieu
Dustin Beaulieu
1,279 Points
Dustin Beaulieu
Dustin Beaulieu
1,279 Points

Thank you for the follow up Steven!