SQL Optimization for Large Datasets | Dataford Interview Questions

Describe your experience with SQL optimization for large-scale datasets. For a hands-on demonstration, write a PostgreSQL query that summarizes qualifying transactions for active accounts during the first quarter of 2025. The result should exclude accounts whose quarterly net amount is not positive.

Output

One row per qualifying active account.
Columns: account_id, account_type, transaction_count, and total_amount.
Include only transactions posted from 2025-01-01 through 2025-03-31, inclusive.
Order by total_amount descending, then account_id ascending.

Schema

accounts

Column	Type	Description
account_idPK	INT	Unique account identifier
account_type	VARCHAR(30)	Deposit or lending account category
status	VARCHAR(20)	Current account status

transactions

Column	Type	Description
transaction_idPK	INT	Unique transaction identifier
account_id	INT	Account associated with the transaction
posted_at	DATE	Date the transaction posted
amount	DECIMAL(12,2)	Signed transaction amount
transaction_type	VARCHAR(20)	Transaction classification

Your question is SQL Optimization for Large Datasets. Start with the requirements and the two tables in the Question tab.

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Problem