Carry Forward the Thermostat Setting

SQLMediumMid level~15 min

Problem

A smart thermostat writes a log row every time it is checked, ordered by an increasing `reading_seq`. It only records a `target_temp` when someone changes the setting; if the setting was left untouched, the row stores NULL.

Write a query that fills in every NULL `target_temp` with the most recent non-NULL `target_temp` from an earlier reading (the setting that was still in effect). The first reading is guaranteed to have a non-NULL value.

Return the columns `reading_seq` and `target_temp`, in order of `reading_seq`.

Tables

Example rows — the live problem includes the full dataset.

ThermostatLog

reading_seq	target_temp
1	Warm 72F
2
3

Expected output

Your answer should return 6 rows with the columns reading_seq, target_temp.

Starter code (SQL)

SELECT *
FROM ThermostatLog;

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