Pivot Sensor Readings Into One Row Per Device

Problem

An IoT platform stores readings in a tall format. Table `readings` has `(device_id, gauge, value)`, where `gauge` is the name of a measurement station and `value` is the reading that device produced at that station.

Reshape the data into a wide format: output `device_id` as the first column, then one column for each distinct gauge name (sorted alphabetically), holding that device's `value` at that gauge, or NULL if the device has no reading there. There is at most one reading per (device, gauge).

For this dataset the gauges are: `Alpha`, `Bravo`, `Delta`, `Echo`. Report one row per device.

Tables

Example rows — the live problem includes the full dataset.

Expected output

Your answer should return 3 rows with the columns device_id, Alpha, Bravo, Delta, Echo.

Starter code (SQL)

SELECT *
FROM readings;

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