Compare Period Metrics With Window Functions | Dataford Interview Questions

Write a SQL query to compare current-period metrics against prior-period metrics using window functions.

Use the provided reporting periods and metric observations. Compare each observation with the preceding available period for the same desk.

Output

One row per desk and reporting period
Columns: desk_name, period_name, current_metric, prior_metric, and metric_change
Include the first observation for each desk with NULL prior values
Order by desk name, then period start date

reporting_periods

Column	Type	Description
period_idPK	INT	Unique reporting-period identifier
period_name	VARCHAR(20)	Readable reporting-period label
period_start	DATE	Start date used for chronological ordering

desk_period_metrics

Column	Type	Description
metric_idPK	INT	Unique metric observation identifier
desk_name	VARCHAR(40)	Desk associated with the observation
period_id	INT	Referenced reporting period
metric_value	DECIMAL(12,2)	Metric value for the desk and period

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