Big Data SQL and Python Concepts | Dataford Interview Questions

Explain the big data concepts you would use when working with SQL and Python in a data engineering role.

For the SQL portion, use the provided account and transaction data to demonstrate scalable filtering, joining, aggregation, null handling, and conditional classification.

Output

One row per active account.
Columns: account_id, account_type, transaction_count, total_amount, and risk_band.
Include only approved transactions dated from 2025-01-01 through 2025-03-31 in the metrics.
Preserve active accounts with no qualifying transactions, using zero totals.
Sort by total_amount descending, then account_id ascending.

Schema

accounts

Column	Type	Description
account_idPK	INT	Unique account identifier
account_type	VARCHAR(30)	Account product type
status	VARCHAR(20)	Current account status

transactions

Column	Type	Description
transaction_idPK	INT	Unique transaction identifier
account_id	INT	Account associated with the transaction
transaction_date	DATE	Business date of the transaction
transaction_status	VARCHAR(20)	Transaction processing status
amount	NUMERIC(12,2)	Transaction amount

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Problem