Complex Data Integration and Joins Questions

Handling intricate join scenarios: multi-condition joins, conditional joins with complex logic, joining on date ranges or overlapping time periods, complex left joins with multiple filtering conditions, self-joins for hierarchical or relationship data, handling non-standard relationships between tables. Understanding implications of different join types on row counts, NULL values, and duplicate handling. Designing queries that correctly integrate data from multiple sources while maintaining data integrity and avoiding duplicate counting or missing data.

MediumTechnical

0 practiced

You join a sales table to a returns table to compute net revenue. Returns can reference orders partially or fully and some returns have multiple credit memos for the same order. Outline SQL patterns to avoid double-counting returns: aggregate returns by order_id first, match at order granularity, and reconcile mismatches. Provide sample SQL.

HardSystem Design

0 practiced

Hard: You must join streaming datasets where schema evolves (fields renamed/moved). As a data analyst designing batch joins for historical reporting, outline a resilient schema mapping strategy, including versioned schemas, canonical column mapping, and join-time transformation rules. Give an example of SQL/ETL mapping logic.

MediumTechnical

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Provide SQL demonstrating how to safely join when one table uses timezone-aware timestamps and the other uses UTC naive timestamps. Tables: events_utc(event_time_utc TIMESTAMP), logs_local(log_time TIMESTAMP WITH TIME ZONE). Show canonicalization steps and explain why mismatched timezones lead to missing joins.

HardTechnical

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Write SQL to join a large fact table to a small dimension in Redshift. Explain how distribution styles and sort keys affect join performance and which distribution style you would choose for the dimension vs the fact. Provide recommended DDL hints.

EasyTechnical

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You have an employees table:

employees(emp_id INT, name TEXT, manager_id INT)

. Write a SQL query to return rows of employee -> manager pairs with both names. Include employees whose manager_id is NULL (show manager_name as NULL or 'No Manager'). Implement this with a self-join and explain aliasing choices.

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