P76Data CleaningIntermediateDiagnose14 min
Diagnose Duplicate Customer Rows After Data Cleaning
Diagnose unexpected duplicate customer rows by tracing keys, source grain, and merge behavior.
#diagnose#duplicates#data grain
Scenario
A cleaned customer table has 10,240 rows but only 9,880 unique customer_id values. Some IDs occur twice after an orders merge.
Problem statement
Identify the most likely failure, support it with compact evidence, and name the next validation check.
Your Task
- Compare row and unique-key counts.
- Inspect duplicate-key examples and source grain.
- Distinguish inconsistent keys, one-to-many data, and a merge error.
Evidence
customers_clean: 10,240 rows; 9,880 unique customer_id
orders source: multiple rows per customer
customer_id C1042 appears twice after merge
Related Concepts
Data grainMerge validationDuplicate keys
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