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Wellington Souza
3,121 PointsYour 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
216,057 PointsDon't restrict your count.
You're already grouping by genre, so just count the rows ("COUNT(*)" or "COUNT(1)").
Dustin Beaulieu
1,278 PointsI 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
216,057 PointsI believe the challenge wants to see the null genre included, so you need an unrestricted count and no filter ("WHERE" clause).
Dustin Beaulieu
1,278 PointsThank you for the follow up Steven!
Dustin Beaulieu
1,278 PointsDustin Beaulieu
1,278 PointsThis worked but I do not understand why the result is different. Can you elaborate on this?
Steven Parker
216,057 PointsSteven Parker
216,057 PointsThe
COUNTfunction only counts rows that have aNOT NULLvalue in the field(s) you specify as an argument, so the original query didn't return the right count for the null genre.