IGNORE NULLS
A sensor fails now and then and temp_c is NULL. IGNORE NULLS makes last_value skip those rows.
task
For device 1 return ts, temp_c and last_temp, the latest non-NULL temp_c up to each row. First 200 rows by ts.
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A sensor fails now and then and temp_c is NULL. IGNORE NULLS makes last_value skip those rows.
For device 1 return ts, temp_c and last_temp, the latest non-NULL temp_c up to each row. First 200 rows by ts.