Design for High-Transactional Data Flow | Dataford Interview Questions

What is your experience with high-transactional data flow in databases?

Using the provided transaction and event data, write a PostgreSQL query that summarizes transaction flow by hour and excludes hours with fewer than two transactions.

Output

Return one row per included hour with flow_hour, total_transactions, successful_transactions, success_rate_pct, avg_latency_ms, and max_latency_ms.
Sort by transaction count descending, then hour ascending.

Schema

transactions

Column	Type	Description
transaction_idPK	INT	Unique transaction identifier
occurred_at	TIMESTAMP	Timestamp when the transaction entered the flow
transaction_type	VARCHAR(30)	Transaction classification
source_system	VARCHAR(40)	System that originated the transaction
amount	NUMERIC(12,2)	Transaction amount

transaction_events

Column	Type	Description
event_idPK	INT	Unique event identifier
transaction_id	INT	Referenced transaction identifier
status	VARCHAR(20)	Processing outcome
latency_ms	INT	Processing latency in milliseconds

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Problem