Running Total and Day-Over-Day Change | Dataford Interview Questions

Write a SQL query to calculate a running total of daily sensor readings and compare it to the previous day at Keysight Technologies.

Use the sensor_readings table. Calculate results independently for each sensor, including days whose readings aggregate to zero or NULL.

Output

One row per sensor and reading date.
Columns: sensor_id, reading_date, daily_reading, running_total, previous_day_reading, and change_from_previous_day.
Include all sensor dates, order by sensor_id and reading_date, and use NULL when no prior day exists or the comparison cannot be calculated.

sensor_readings

Column	Type	Description
sensor_reading_idPK	INT	Unique identifier for a raw sensor reading
sensor_id	VARCHAR(20)	Keysight measurement sensor identifier
reading_date	DATE	Calendar date of the reading
reading_value	DECIMAL(10,2)	Sensor reading value

Your question is Running Total and Day-Over-Day Change. Start with the requirements and the one table in the Question tab.

Run and submit as often as you like. When you're ready, talk me through your approach or go straight to the code.

Write a SQL query to calculate a running total of daily sensor readings and compare it to the previous day at Keysight Technologies.

Use the sensor_readings table. Calculate results independently for each sensor, including days whose readings aggregate to zero or NULL.

One row per sensor and reading date.
Columns: sensor_id, reading_date, daily_reading, running_total, previous_day_reading, and change_from_previous_day.
Include all sensor dates, order by sensor_id and reading_date, and use NULL when no prior day exists or the comparison cannot be calculated.

sensor_readings

Column	Type	Description
sensor_reading_idPK	INT	Unique identifier for a raw sensor reading
sensor_id	VARCHAR(20)	Keysight measurement sensor identifier
reading_date	DATE	Calendar date of the reading
reading_value	DECIMAL(10,2)	Sensor reading value

Your question is Running Total and Day-Over-Day Change. Start with the requirements and the one table in the Question tab.

Run and submit as often as you like. When you're ready, talk me through your approach or go straight to the code.