First and last track per listener

Constraints

1. 1Exactly one row per listener. A listener with seven plays still returns one row.
2. 2first_track is the title of their earliest play by played_at; last_track is the title of their latest.
3. 3A listener whose earliest and latest plays are the same track shows that title twice — u6 does, and that is correct rather than a duplicate to remove.
4. 4No two plays by one listener share a timestamp, so both ends are unambiguous.
5. 5Order by user_id.

Worked example

u2 starts with Static Bloom on 6 January and ends with Night Signal on 5 March, so the row is one line: u2, Static Bloom, Night Signal. Write LAST_VALUE(title) OVER (PARTITION BY user_id ORDER BY played_at) with no frame clause and the query returns 22 rows instead of 7. The default frame ends at the current row, so last_track becomes the running latest — a different value on every play, and nothing for DISTINCT to collapse.

What this tests

Window frames in the form that bites hardest: under the default frame FIRST_VALUE is correct by accident and LAST_VALUE is wrong by default, so the frame has to be stated rather than assumed.