SQL for Beginner - Solutions Group By

.sql

-- QUIZ 1
-- count number of songs by genre
SELECT 
  genres.name,
  COUNT(*) AS n
FROM genres
JOIN tracks
  ON genres.genreid = tracks.genreid
GROUP BY genres.name;

-- QUIZ 2
-- sum invoices by country
SELECT 
  customers.country,
  SUM(total) AS sum_invoice
FROM customers
JOIN invoices
  ON customers.customerid = invoices.customerid
GROUP BY customers.country;