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SQL practice question · Hard · Window Functions · Amazon

machine_events logs server state changes (server_id, event_time, event_type) where event_type is 'start' or 'stop'. For each server, order its events by time and pair every 'start' with the server's next event when that next event is a 'stop'; a 'start' with no following 'stop' is ignored. Sum the paired durations. Output columns: server_id, uptime_hours (rounded to 2 decimals). Order by server_id ascending.

Table: machine_events

Schema of machine_events
ColumnType
server_idINTEGER
event_timeTIMESTAMP
event_typeTEXT
Sample rows of machine_events
server_idevent_timeevent_type
12026-01-01 09:00:00start
12026-01-01 12:00:00stop
12026-01-02 08:00:00start
12026-01-02 10:30:00stop
22026-01-01 10:00:00start
22026-01-01 11:15:00stop
Expected output on the sample data
server_iduptime_hours
15.5
21.25

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