Client Retention Over Time | Dataford Interview Questions

How would you analyze client retention over time using SQL for TaskRabbit?

Use completed TaskRabbit tasks to identify each client's first active month and measure whether that client completed tasks again in later months.

Output

One row per cohort month and activity month for clients with at least one completed task.
Return cohort_month, activity_month, cohort_size, active_clients, and retention_rate.
Sort by cohort_month, then activity_month, both ascending.

clients

Column	Type	Description
client_idPK	INT	Unique TaskRabbit client identifier
client_name	VARCHAR(100)	Client display name

tasks

Column	Type	Description
task_idPK	INT	Unique task identifier
client_id	INT	Client who requested the task
status	VARCHAR(30)	Current task status
completed_at	TIMESTAMP	Timestamp when the task was completed

Your question is Client Retention Over Time. Start with the requirements and the two tables in the Question tab.

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