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Troubleshoot Duplicate Rows After Joins

HardSQL & Data Manipulation00:00
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Your question is Troubleshoot Duplicate Rows After Joins. Take a moment with it on the right.

Talk me through your thinking if you like. When you're confident, submit your answer and I'll grade it like a real screen (7/10 or better passes).

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Problem

Context

You are reviewing a workflow that joins several tables and returns more rows than expected. This usually means one or more joins are not one-to-one, or a filter is being applied after row multiplication.

Core question

Explain how you would troubleshoot the workflow and identify which join is introducing duplicates. Describe how you would verify join cardinality, spot many-to-many relationships, and distinguish true duplicates from repeated business keys.

Scope guidance

Focus on the SQL reasoning you would use to isolate the problem, not on generic ETL advice. A strong answer should cover join keys, uniqueness checks, intermediate row counts, and how you would fix the issue without losing valid records.