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
Two vendors provide product catalogs with different item identifiers and overlapping but inconsistent attributes. Describe how you would build a canonical product table and join both vendor feeds into it to avoid double-counting sales. Include matching strategy, canonical key generation, confidence scoring, and how to surface ambiguous matches to business owners.
MediumTechnical
0 practiced
A business asks: "Why do our weekly revenue numbers change after we add a new join between orders and a refunds table?" As a data scientist, explain likely reasons (join cardinality, nulls, missing keys, multiple refunds per order causing duplication), how to investigate (row counts pre/post join, sample joins), and steps to correct aggregation logic.
HardTechnical
0 practiced
Given two very large tables to be joined on multiple columns, describe how you would interpret and act upon a query plan that shows a Nested Loop Join instead of Hash Join, causing very slow execution. What causes this choice and how would you change statistics, hints, or rewrite the query to encourage a more efficient plan?
HardTechnical
0 practiced
Design a test harness and a set of automated tests to validate the correctness of join logic in a production ETL job that merges orders with customer segments. Tests should cover row counts, duplicate detection, null handling, boundary-time matching, and data lineage. Include SQL assertions and end-to-end test ideas.
EasyTechnical
0 practiced
Consider this query (PostgreSQL):SELECT c.customer_id, o.order_idFROM customers cLEFT JOIN orders o ON c.customer_id = o.customer_idWHERE o.status = 'SHIPPED';Explain why this LEFT JOIN behaves like an INNER JOIN in practice and rewrite the query to correctly return all customers with shipped orders while preserving other customers with NULLs (i.e., customers with no orders must still appear).
Unlock Full Question Bank
Get access to hundreds of Complex Data Integration and Joins interview questions and detailed answers.
Sign in to ContinueJoin thousands of developers preparing for their dream job.