SQL MoM Growth by Channel | Dataford Interview Questions

Write a SQL query to find the month-over-month growth rate of new user registrations by marketing channel at Guideline. Use the provided registration and marketing channel data. Return monthly results, including a null growth rate when a channel has no prior month for comparison.

Output

One row per marketing channel and registration month.
Columns: channel_name, registration_month, new_registrations, previous_month_registrations, and mom_growth_pct.
Include all available registration months, sort by channel_name ascending and registration_month ascending, and round growth percentages to two decimal places.

Schema

registrations

Column	Type	Description
registration_idPK	INT	Unique registration event identifier
user_id	INT	Identifier of the newly registered user
channel_id	INT	Marketing channel associated with the registration
registered_at	TIMESTAMP	Timestamp when the user registered

marketing_channels

Column	Type	Description
channel_idPK	INT	Unique marketing channel identifier
channel_name	VARCHAR(100)	Display name of the marketing channel

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Problem