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Why is the a NULL genre value complicating this challenge and howto solve it elegantly?
So this was my query to find the count of all unique genres in books:
SELECT COUNT(*) AS 'total_genres' FROM (SELECT DISTINCT genre FROM books) G;
Now this returned 7 which i figured eventually was one more than the actual number because of NULL values in some rows for genre... So this worked:
SELECT COUNT(*)-1 AS 'total_genres' FROM (SELECT DISTINCT genre FROM books) G;
But this seems like a recreational solution... Is there a nicer more robust way to solve this?
I was too lazy to scroll down and put the answer in the corresponding field and just used the comment field instead (that's why you could not mark it as the correct solution)... :-) I am glad to be of help, if you don't know the reason why this works - just let me know.
But here is the solution again:
SELECT COUNT(*) AS 'total_genres' FROM (SELECT DISTINCT genre FROM books WHERE genre IS NOT NULL)