SQL Monthly Volume Comparison | Dataford Interview Questions

Write a SQL query to calculate monthly operational volume and compare it to the prior month.

Use operational_events and operation_types. Include only events with a valid operation type and a non-null event date. Treat the prior month as the preceding reported month for the same operation type.

Output

One row per operation type and reported month.
Columns: operation_type, monthly_period, monthly_volume, prior_month_volume, volume_change, and percent_change.
Include NULL comparison values when no prior reported month exists. Order by operation_type, then monthly_period.

Schema

operational_events

Column	Type	Description
event_idPK	INT	Unique operational event identifier
operation_type_id	INT	Referenced operation type
event_date	DATE	Date on which the operational event occurred

operation_types

Column	Type	Description
operation_type_idPK	INT	Unique operation type identifier
operation_name	VARCHAR(100)	Name of the operational activity

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