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The optimal approach uses SQL aggregation with GROUP BY on month and country. Approved transactions are counted using conditional aggregation, while chargebacks are identified through a join with the chargebacks table.
Database aggregation and reporting queries similar to Monthly Transactions II are common in technical interviews, especially for data-focused roles. They test your understanding of SQL joins, grouping, and analytical queries.
Key SQL concepts include GROUP BY, JOIN operations, conditional aggregation, and date formatting. These allow you to calculate monthly summaries and separate approved transactions from chargebacks.
In SQL problems like this, the focus is on relational operations rather than traditional data structures. Efficient grouping, joining tables, and conditional aggregation are the main techniques used to compute the required metrics.