REVIEW: just some nitpicking

[camelPhonso]

• keep iteration in mind: you've aimed a really cool functionality (submitting music with urls) but the app at the moment has no option to submit anything at all. For the sake of managing expectations it'd have been better to let users submit a song title and then iterate on that functionality to your ideal
• be mindful of the readability of your code: for example, the code below feels cleaner because table names have been shortened, but for a new developer looking at the code it means a bit of guessing (or moving between files to check the schema) to understand what tables are being referred

SELECT
  p.id AS post_id,
  p.artist,
  p.song,
  u.name AS user_name,
  p.posted_at

• relations between tables: your posts table has a user_id column but when users log into the page they get a list of all posts. This would have been a quick win if you let users see their own posts only (considering the learning outcomes)