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Databases Reporting with SQL Aggregate and Numeric Functions Counting Groups

Posted by Derek Morse
Derek Morse
1,776 Points

NOT understanding

SELECT COUNT genre FROM books GROUP BY genre_count;

2 Answers

Tomas Schaffer
Tomas Schaffer
11,606 Points
Tomas Schaffer
Tomas Schaffer
11,606 Points

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

But what is the reason to group the results of one column? Because this query is the result of one record.

This Query counts the number of result.

SELECT COUNT(*) genre_count FROM books;

So this is the same with better performance because you dont select all data just counting rows of table:

SELECT COUNT(0) genre_count FROM books;

Steven Parker
Steven Parker
231,268 Points
Steven Parker
Steven Parker
231,268 Points

Did you actually try any of those as answers to the challenge? :see_no_evil:

Tomas Schaffer
Tomas Schaffer
11,606 Points
Tomas Schaffer
Tomas Schaffer
11,606 Points

You didn't put the link to challenge. I didn't even know thats from challenge. But i work with PostgreSQL. So post the link to challenge if you like to.

Steven Parker
Steven Parker
231,268 Points
Steven Parker
Steven Parker
231,268 Points

The link to the challenge is the colored button in the upper right of this page that says "View Challenge".
The system put it there automatically when Derek created this question.

Tomas Schaffer
Tomas Schaffer
11,606 Points
Tomas Schaffer
Tomas Schaffer
11,606 Points

OK I am sorry didnt se the button.This is the correct answer.

SELECT genre, count(0) as genre_count FROM books GROUP BY genre;

Tomas Schaffer
Tomas Schaffer
11,606 Points
Tomas Schaffer
Tomas Schaffer
11,606 Points

I didn't see first time button to Challenge and didn't see whole question. The right Answer to Challenge is below Derek.

SELECT genre, count(0) as genre_count FROM books GROUP BY genre;