MoM Growth in Support Channels | Dataford Interview Questions

Wayfair wants to compare how effectively customers are resolved through self-service experiences and live agent support. Write a PostgreSQL query that reports monthly resolved interactions for both channels and their month-over-month growth.

Requirements

Join interaction logs to active Wayfair customers only.
Count interactions where resolved = TRUE separately for self_service and live_agent.
Calculate month-over-month percentage growth for each channel using LAG.
Return one row per month from January through April 2024, ordered chronologically. Return NULL growth when no prior month exists or the prior count is zero.

Schema

customer_profiles

Column	Type	Description
customer_idPK	INTEGER	Unique customer identifier
customer_name	VARCHAR(100)	Customer display name
customer_status	VARCHAR(20)	Customer lifecycle status

interaction_logs

Column	Type	Description
interaction_idPK	INTEGER	Unique interaction identifier
customer_id	INTEGER	Customer associated with the interaction
occurred_at	TIMESTAMP	Timestamp when the interaction occurred
interaction_type	VARCHAR(20)	Support channel used by the customer
resolved	BOOLEAN	Whether the interaction was resolved

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Problem