Hottest Reading per Sensor

Return each sensor with its highest temperature. Order by sensor.

Table schema

Readings(sensor VARCHAR(5), ts DATETIME, temp INT)

Sample data

sensor | ts | temp
S1 | 2026-08-01 10:00:00 | 20
S1 | 2026-08-01 11:00:00 | 27
S1 | 2026-08-01 12:00:00 | 25
S2 | 2026-08-01 10:00:00 | 30
S2 | 2026-08-01 11:00:00 | 31
S2 | 2026-08-02 10:00:00 | 22