Project Data Collection With SQL | Dataford Interview Questions

Tell me about your projects and how you collect, clean, and manipulate data using SQL.

Use the provided project, batch, and cleaning-event tables to demonstrate the SQL work behind that process. Write a query that summarizes first-quarter 2025 collection and cleaning activity for every project.

Output

One row per project, including projects without qualifying batches.
Return project_id, project_name, collected_rows, valid_rows, cleaned_rows, validation_rate, and latest_cleaned_at.
Treat missing numeric totals as zero, return NULL for validation_rate when no rows were collected, and order by project_id ascending.

Schema

projects

Column	Type	Description
project_idPK	INT	Unique project identifier
project_name	VARCHAR(100)	Project name
owner_name	VARCHAR(100)	Project owner

data_batches

Column	Type	Description
batch_idPK	INT	Unique collected data batch identifier
project_id	INT	Project associated with the batch
source_name	VARCHAR(100)	Data collection source
collected_at	DATE	Date the batch was collected
rows_collected	INT	Number of rows collected
rows_valid	INT	Number of rows passing validation

cleaning_events

Column	Type	Description
event_idPK	INT	Unique cleaning event identifier
batch_id	INT	Batch affected by the event
event_type	VARCHAR(50)	Type of cleaning or validation action
affected_rows	INT	Number of rows affected
event_date	DATE	Date of the cleaning event

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Problem